Showing papers in "American Journal of Botany in 1967"

The role of auxins and cytokinins in the release of buds from dominance

Abstract: The paper deals with the general problem of the physiological basis of branching, and the roles of known and unexplored factors in sensitivity to apical domirnance. It is shown that when pea seedling shoots are completely or partially inhibited by other shoots on the same plant auxin can promote their elongation, even though it does not have this effect on inhibited buds. This influence of auxin is only exerted on internodal elongation and not on apical growth. When kinetin in a solution of alcohol and carbowax is applied directly to the lateral buds of pea seedlings, it releases them from inhibition by the growing apex. It is shown that the role of alcohol in this solution is to act as a surfactant, permitting good contact with the buds, while that of carbowax, being hygroscopic, is to maintain a thin film of solution over the buds. Buds thus released from apical dominance by kinetin do not elongate as much as do uninhibited control buds. Such kinetintreated buds can, however, be made to elongate normally by the application of auxin locally to their apices. It is concluded that growing shoots are relatively insensitive to correlative inhibition because they synthesize two types of growth substances, namely, auxin, which antagonizes the inhibitory effect on internodal elongation, and cytokinins, which permit the apex itself to develop. In the discussion it is brought out that many cases of branching, which appear at first to bear little relation to one another, can be understood on the basis of two principles, namely: (1) Any reduction in the growth rate of a dominant apex reduces its inhibitory effect on other apices, and (2) once an apex starts growing it becomes less sensitive to inhibition by other apices These generalizations and the experimental results are tentatively interpreted in terms of an interaction between the syntheses of auxin and of cytokinin.

The distribution and phylogenetic significance of binucleate and trinucleate pollen grains in the angiosperms

Abstract: A B S T R A C T Studies of the cytology of angiosperm pollen which extend our knowledge of the distribution of binucleate and trinucleate pollen to almost 2,000 species of flowering plants are summarized. Approximately 70% of the species studied release pollen in a binucleate stage, and none of them shed both types of pollen as a constant varietal trait. All phylogenetically primitive taxa are binucleate. The trinucleate trait evidently has originated independently at many times during angiosperm evolution. In no instance must one infer the origin of binucleate taxa from trinucleate ancestors. Most genera are monotypic with respect to pollen cytology, and only 10 genera are known to include both binucleate and trinucleate species. Among the 265 families studied, 179 include only binucleate genera and 54 include only trinucleate genera, while 32 include both types. Nearly all aquatic species with submersed flowers shed pollen in a trinucleate stage. A group of physiological differences which distinguish binucleate and trinucleate pollen is reviewed in relation to the survival and possible selective advantage of trinucleate mutants, and the significance of the binucleate pollen grain in the origin and evolution of flowering plants is discussed.

Surface area relations of woody plants and forest communities

Abstract: A B S T R A C T Surface area of wood and bark is an important dimension of forests, with implications fol respiration rate, energy exchange, and water and mineral budgets. Surface area of stem wood and bark can be estimated effectively from linear regressions on conic surface (one-half basal circumference times tree height) or from regressions of the logarithm of area on the logarithm of diameter at breast height. Branch surface can be estimated from a formula using branch basal diameter, length, and number of current twigs, and from logarithmic regressions of branch bark surface on basal diameter of branches and breast-height diameter of trees. In temperate deciduous forests several square meters of plant surface occur above each square meter of ground surface; these plant surfaces include 0.3-0.6 m2 of stem bark, 1.2-2.2 m2 of branch bark, and 3.0-6.0 m2 of leaf blades. Branch bark surface increases more rapidly than leaf surface with increasing size of branches and trees. Growth and aging of trees, and maturation of forests, imply increasing ratios of bark (and wood) surface to the photosynthetic leaf surface which supports its growth and respiration. ONE OF THE MOST difficult dimensions of an organism to measure is that which might seem most accessible to measurement-the area of its outer surface. Evolution of the form of the surface tends normally toward the minimum area of protective covering consistent with the organism's structural design and requirements for interchange with environment. Economy in surface of a complex structure is likely to imply geometric complexity of the surface. Is it possible, without full solution of this geometric complexity, to find reasonable approximations of surface area? Estimates are likely to involve either logarithmic regressions of surface area on diameter or other easily measured dimensions, or correction factors from surface area estimates based on a simplified geometry of the organism, or combinations of these. This paper considers ways of estimating above-ground surface areas of woody plants and the interest of these surface areas for the functional ecology of forests and shrublands.

Chromosome complement as a determinant of the morphogenic potential of tobacco cells

Abstract: A B S T R A C T Polysomatism in Nicotiana tabacum L. 'Wisconsin 38' was confirmed. Pith samples from the region of the stem 3.5-10.5 cm below the apex contained nearly equal proportions of diploid and tetraploid cells and samples obtained further down, 15.5-22.5 cm, showed predominantly tetraploid (circa 70%) and smaller proportions of diploid (9%), octaploid (16%), and aneuploid (5%) cells. Cultures of the callus from pith explants showed no evidence of diploid cells after 1 year, but did show roughly half 4n and 8n euploid and half -aneuploid cells. The callus after 6 years in vitro consisted entirely of aneuploid cells. The attainment of this predominance of aneuploid cells could account for the decline of callus growth and organ formation of tobacco tissue cultures. Tobacco tissue cultures started from single cells disclosed that totipotentiality was not restricted to diploid cells but was possessed by and expressed with apparently equal ease by tetraploid cells. The morphogenetically depressed situation was associated with a highly variable aneuploidy. With increase in somatic age the frequency of aneuploid cells increased and the level of ploidy among the aneuploid cells shifted from sub-tetraploidy to above tetraploidy.

Origin of Fragaria polyploids. I. Cytological analysis

Abstract: Leaves of resistant and susceptible breeding lines of two closely related varieties of cabbage, 'Glory' and 'Globe,' showing internal tipbum were examined anatomically. Since both resistant and susceptible lnes developed tipburn, the type of injury rather than the amount was considered. Regardless of the degree of resistance, cellular disorders in the tipburned areas were the same. Early symptoms showed small gray areas at the lobes of the leaves. The outer parenchymatous cells of these areas remained normal. Some of the xylem vessels became occluded with a granular substance; surrounding cells, including the idioblasts, enlarged. The idioblasts, reported to contain the enzyme myrosin, contained a particulate substance. Some idioblasts hypertrophied and also divided resulting in the distribution of the particles to additional cells. The conditions causing tipburn also affected cell walls, causing thickening and the production of pectic warts between cells and on walls facing the intercellular spaces. As more xylem vessels became occluded, and as the number of idioblasts with particles increased, the cells at the periphery of the leaf collapsed. INTERNAL TIPBURN of cabbage has plagued growers for some time, but the exact cause of this disorder has not been established. Investigators agree that the cause is not a pathogen. As reviewed by Natti and Atkin (1962), conditions that have been reported as causes of tipburn include high and low amounts of certain elements, environmental conditions, and cultural practices such as time of planting and harvest. Walker, Edgington, and Nayudu (1961) showed that compared to normal heads, tipburned cabbage heads had a lower Ca content and that the amount of Ca in interior leaves was much lower than in the outer leaves, and leaf marginal tissue contained the least. High soil moisture and poor drainage contributed to the severity of the disorder. Maynard, Gersten, and Vernell (1965) studied the effect of levels of Ca on a resistant and a susceptible variety of cabbage and found that tipburn was related to low Ca content in the tissue. Under stress conditions the resistant variety was able to transport and accumulate more Ca than the susceptible one. They suggested that this possibly resulted from genetic variability. The selection of varieties resistant to tipbum has been Received for publication February 23, 1966. Published with the approval of the director of the Agricultural Experiment Station. reported and is in progress by Walker, Williams, and Pound (1965). Natti and Atkin (1962) were planning a breeding program designed to select F1 hybrids of cabbage that would be resistant to internal tipburn and other diseases. Considerable attention has been focused on the causes of internal tipburn, but the internal cellular responses have not been investigated. Consequently, this i.nvestigation was conducted to determine what abnormal cellular responses occurred. MATERIALS AND METHODS-In 1961 samples of marginal leaf tissue showing mild and severe tipburn symptoms were taken from eight fieldgrown mature heads of resistant and susceptible lines derived from the variety 'Glory.' In each of the following 3 years samples were taken from resistant and susceptible lines derived from the variety 'Globe.' The extent of internal tipburn was not considered in the resistant and susceptible varieties; only the anatomical responses were studied. The leaves were fixed in formalin-aceticalcohol or Craf (Nawaschin type III) solutions. Marginal areas of healthy tissue were used for comparison. The fixed leaves were dehydrated with n-butyl alcohol, infiltrated and embedded in Paraplast (Aloe Scientific, Division of Brunswick, St. Louis 3, Mo.). Sections were cut 10 ,u thick on a This content downloaded from 207.46.13.153 on Fri, 05 Aug 2016 05:44:13 UTC All use subject to http://about.jstor.org/terms

The chloroplast structure of iojap maize

Abstract: A B S T R A C T The ultrastructure of the plastids from the genetically caused but maternally transmitted mutant iojap of maize was studied at four stages of development. The plastids of green and potentially green tissue were normal at all stages studied. The plastids of the white tissue were aberrant at all stages studied and lacked the normal grana-fretwork system as well as a normal prolamellar body. DNA-like fibrils were present in aberrant plastids, but ribosomes were absent. This indicates that chloroplast ribosomes are important in chloroplast membrane formation. Aberrant plastids fail to develop normally and are not a degeneration of normal plastids. Aberrant and normal plastids occur in single cells in green tissue, but only aberrant plastids have been

The molecular organization of chloroplast membranes

Abstract: The presence of subunits in chloroplast membranes is suggested by polarization, fluorescence, and X-ray studies Subunits (quantasomes) may be observed in the electron microscope on dried shadowed membranes and in replicas of membranes produced by the freezeetching technique Regular subunits are also observed with the electron microscope in thin sections of chloroplast membranes Chemical considerations suggest that many membranes are composed of lipoprotein subunits Thin sections reveal two types of chloroplast membranes, the fret membranes composed of one layer of subunits, and the partitions composed of two layers of subunits Chloroplast membranes consist of about 451% protein and 551% lipid Some 80% of the lipids are the highly surfactant glycolipids In this paper the subunits are visualized as assymetric lipoproteins, probably having a protein core surrounded by componeilts determined by the nature and environment of the membrane Since the stroma, fret channels, and loculi contain aqueous materials, it is further postulated that the membranes bordering these spaces bind the highly surfactant glycolipids The region between the two rows of subunits in the partition appears to be highly hydrophobic, rich in chlorophyll, and low in glycolipids Some chlorophyll also may occur within the subunits both in the partitions an(d in the fret membranes Since four subunits appear to comprise a quantasome, at least two types of forces, inter- and intra-quantasome forces, bind the subunits together in sheets Chloroplast membranes thus differ from a "unit membrane" in two important respects: (1) they must be an aggregate of globular subunits, and (2) the lipoprotein subunits consist of a protein matrix which binds the chlorophylls and lipids by hydcrophobic association with their hydrocarbon moieties

Ultrastructural changes during zoospore formation in phytophthora parasitica.

Abstract: A B S T R A C T Cleavage of the multinucleate sporangial cytoplasm begiins by a rearrangement and subsequent fusion of randomly dispersed cleavage vesicles The vesicles line up in planes equidistant from neighboring nuclei and along the sporangial wall In addition, they contribute to the enlargement of the central vacuole Fusion of these vesicles with themselves and with the central vacuole cleaves the cytoplasm into uninucleate zoospores, each with two flagella The sporangial wall consists of two layers, an outer thin one which is continuous over the plug of the discharge pore and an inner thick one which tapers off near the plug The plug consists of fibrillar material and is ejected upon release of the zoospores A plug-like structure separating the forming sporangium from the hypha has a homogeneous matrix pervaded with an anastomosing network of fine electron-dense chaiiiels In additioni, glycogen-like granules occur within mitochondria and paired structures are interpreted as procentrioles ZOOSPORE PRODUCTION inl the asexual sporaingia of the fungus Phytophthora parasitica Dast from papaya deserves attention for at least two reasonis First, it provides a model for the cleavage of a multinucleate cytoplasm into uninucleate portions, a process which is accompanied by formation of a new cell membrane around each resultant zoospore Secoind, zoospore production represents a stage in the life cycle which is vulnerable to enviroinmental influences and might provide a key for future control of this inotorious plant pathogen (Waterhouse, 1962)

Chemical control of adventitious organ formation in lactuca sativa explants

Abstract: Both kinetin and adenine promote bud initiation in excised cotyledoins of Lactuca sativa. Controls lacking these substances form abundant roots but have never formed buds. Indoleacetic acid and certain mineral salts are also necessary for regeneration of shoots. Although bud growth from cotyledons is extensive on a medium containing both indoleacetic acid and kinetin, excised roots display a low propensity toward bud formation and typically develop callus tissue with roots. Growth of hypocotyl sections is intermediate with respect to bud formation. Shoot initiation in lettuce thus varies with the region of the seedling as well as with the culture medium. BOTH KINETIN (6-furfurylaminopurine) and adenine (6-aminopurine) promote formation of adventitious buds in several plant species. All such species, however, produce some buds even without added kinetin or adenine (see review, Dore, 1965). The question is open, therefore, as to whether these compounds directly cause cells to become committed to bud formation or simply accentuate the expression of a commitment determined by other factors. Our studies of bud formation in Lactuca sativa bear on this question. LaRue (1933, 1936) failed to obtain any shoot formation from leaves of L. sattiva and L. canadensis. We obtain such formatioin only when adenine or kinetin is present.

Tetraxylopteris schmidtii: its fertile parts and its relationships within the aneurophytales

Abstract: A B S T R A C T The fertile branching system of Tetraxylopteris is composed of successive "nodes" bearing opposite and decussately arranged, upcurved sporangial complexes. By means of the transfer technique the morphology of the sporangial complex was revealed. It consists of a main stalk which dichotomizes twice producing four major branches. Each of the four branches is further subdivided three times, the subdivisions being arranged alternately and pinnately. The ultimate divisions bear the sporangia singly and terminally. The sporangial complexes decrease in size distally and are more tightly curved at the apex. The sporangia are oblong-oval with an acute apex. The spores are identical to the dispersed spore taxon Rhabdosporites langii, Richardson. They are spherical, trilete and pseudosaccate with a fine granular ornament on the pseudosaccus. They are 75-176 , in diameter and show developmental stages from young tetrads to separated, fully mature spores depending on the age of the sporangium from which they were obtained. This is the first account of spores in sporangia of Tetraxylopteris. The diagnosis of the genus and species are emended to include the new information and the order Aneurophytales is redefined. TETRAXYLOPTERIS SCHMIDTII Beck is a primitive member of the Progymnospermopsida (Beck, 1960, 1962). Although its anatomy and vegetative morphology were thoroughly investigated (Beck, 1957), little is known of the morphology of its fertile branches. The present study describes the

A survey of floral anatomy in araceae

Abstract: Flowers of 23 species representing six subfamilies of Araceae were studied by means of serial cross sections, special attention being given to vascular patterns and to taxa of supposed phylogenetic importance. Floral structure is shown to be extremely diverse with no unifying pattern common to all subfamilies. Conclusions include the following: (1) Lysichiton has a specialized gynoecial vascular pattern which differs from others encountered in the survey and which weighs against the primitive position attributed to this genus by Hutchinson. (2) Philodendron, with its multiple stylar canals, cannot have originated from subfamily Pothoideae, as Engler's phylogenetic concept would require of all Araceae; instead, it appears that several synearpous evolutionary lines have evolved independently from extinct apocarpous members of the family. (3) In Acorus, stamens are introrse and dorsal carpellary bundles are lackiing; these characters and others justify the recognition of Acorus as a separate subfamily Acoroideae. In addition, the survey revealed a peculiar deterioration of the inner ovary wall and the septa in several taxa, apparently a normal feature of floral development. Spathiphyllum solomonense Nicolson is described in an appendix. LITERATURE ON comparative anatomy of flowers has accumulated over the past several decades into a sizeable body of information; in Rao's (1961) bibliography of more than 800 entries, most families of angiosperms are represented by at least one publication. It appears, however, that no modern botanist has undertaken a special investigation of vasculature and histology in flowers of Araceae. This is rather surprising, because the family is large and widely distributed with many familiar ornamental species. Moreover, most of the families commonly suggested as allies of Araceae have been studied, at least in an introductory way, from the standpoint of floral structure: al-Rawi (1945), Bosch (1947), and Morrow (1963, 1965) investigated the palms; Harling (1946, 1958) and Garcin (1958), the Cyclanthaceae; Gatin (1920), Anderson (1940), and el-Hamidi (1952), the Liliaceae. The anatomy of araceous flowers is not totally unknown, for the authoritative monographs of Engler (1905, 1911, 1912, 1915, 1920a, 1920b), Krause (1908, 1913), and Engler and Krause (1908, 1920) are replete with drawings and descriptive comments relating to floral structure. For the most part, however, these observations are derived from the earlier works of Schott (in particular his Genera Aroidearum, 1858) and Engler (see especially his 1884 contribution on floral morphology), in which no information is given on vascular patterns. Apparently, the only 19th century worker to examine floral vasculature of Araceae was van 1 Received for publication May 31, 1966. The authors thank Dr. Donald R. Kaplan for reading the manuscript critically. Tieghem (1867), who reported on the -arrangement of bundles in pistillate flowers of Zantedeschia, Alocasia, and Aglaonema, later (1907, p. 315) offering an interpretation of the staminate flower of Aglaonema. Possibly the only contribution since van Tieghem's time is Saunders' (1939) brief commentary, expressed in the terms of her long discredited theory of "carpel polymorphism." We have not found that any author on Araceae has compared vascular systems and other microscopic floral characters in genera selected for possible phylogenetic interest, as we attempt to do in this paper. Our investigation is meant to be no more than an introductory survey. It was planned as a summer project only (the laboratory work was completed during the summer of 1965, while the third author was a research assistant in the Smithsonian Summer Program for Graduate Students), and because of other research commitments we do not expect to carry it further. Our aims are to point out the diversity in internal floral structure of the Araceae, particularly in those groups claimed to be primitive by various authors, to compile pertinent literature, and to raise questions of phylogeny that should be considered in subsequent studies of the family. We hope thus to attract the attention of other investigators to an interesting and, from the anatomical standpoint, neglected group of monocotyledons. Accordingly, the second author will be happy to share his collections of inflorescences with any worker who wishes to use them for further anatomical research. M-ATERIALS-Specimens used in this investigatiorn were selected from an assemblage of about

A synopsis of the genera and species of the tribe theleboleae (= pseudoascoboleae)

Abstract: A B S T R A C T Examination of genera of the Pseudoascoboleae (Ascomycetes, Discomycetes, Ascobolaceae) revealed that many were polytypic. Characters presently used to distinguish these genera are considered to be artificial and true relationships cut across accepted generic lines. Of the genera treated, Thecotheus and parts of Ascophanus, since their asci blue in iodine and their spores bear callose-pectic markings, are considered more closely related to the Pezizeae. Other genera are excluded from the Pseudoascoboleae because of other striking characters. Since the Pseudoascoboleae is shown to be an artificial grouping, it is proposed to abandon the name, using instead the tribe name Theleboleae, placed in the Pezizaceae rather than the Ascobolaceae, for all of those genera with asci that do not blue in iodine, with smooth, elliptical spores without oil guttules, and with eight-spored and multispored species. Four new genera are described: Jodophanus, for species of Ascophanus with iodine-positive asci; Coprotus, for segments of Ascophanus and Ryparobius; Caccobius, for species intermediate to Ascozonus and Thelebolus; and Trichobolus, for the setose members of Thelebolus. The species of Ryparobius not belonging to Coprotus are transferred to Thelebolus. THE ASCOBOLACEAE have been characterized mainly by their relatively broad asci which protrude above the general level of the hymenium as they ripen. The spores commonly lie in two or three irregular rows in the ascus instead of in a single vertical row as in other families. They are mainly dung inhabiting, with a few species on burnt ground, soil, or debris. Boudier (1869) placed all of the hyaline-spored species in the Ascobolei Spurii and listed three genera: Ascophanus with 8- to 16-spored asci, and Thecotheus and Ryparobius with multispored asci. Thecotheus was distinguished from Ryparobius by its prominent paraphyses and huge asci and spores. With few exceptions subsequent workers have followed Boudier in dividing the subfamily basically on spore number and size.

Angiosperm wood from the upper cretaceous of central california. iii

Abstract: A B S T R A C T Three species of fossil wood representing two genera are described. The specimens are from a collection of woods from the Upper Cretaceous Panoche formation of central California. Tetracentronites panochetris sp. nov. resembles angiosperm wood in ray structure and vascular pitting but lacks vessels. Plataninium platanoides sp. nov. is similar to the wood of Platanus, and the evidenee presented points to a direct relationship. The resemblance between Plataninium californicum sp. nov. and the woods of certain Icacinaceae is discussed, but evidence of relationship is inconclusive. THE SPECIMENS here described are a part of an assemblage of angiosperm woods collected from Upper Cretaceous marine sediments in central California discussed in an earlier paper (Page, 1967). In this assemblage of woods five specimens were found which resemble the wood of Platanus but differ in one or two important features. In a survey of modern woods the general pattern shared by the fossils and Platanus appeared in several unrelated genera, but in no case did the fossil correspond exactly with wood of a modern genus. Yet, all these woods have more in common with each other than with any others. For this reason the circumscription of Plataninium Unger emend. Vater (1884) is extended to encompass the range of variation exemplified by these genera. DIAGNOSIS-Plataninium Unger emend. Vater emend. Page-A form genus for fossil woods resembling certain members of the Fagaceae (Fagus), Platanaceae (Platanus), Eupteleaceae (Euptelea), and Icacinaceae (Citronella, Ottoschultzia), whose familial relationships cannot be determined with certainty, but which have these structural features: solitary pores, scalariform to opposite vessel pitting, scalariform or scalariform-simple perforation plates, broad rays up to 10 or more cells wide and more or less homogeneous, apotracheal parenchyma diffuse or in short uniseriate tangential lines.

Abscisin, auxin, and gibberellin effects on the developmental aspects of abscission in cotton (gossypium hirsutum)

Abstract: The effects of accelerating and retarding amounts of abscisin (Ab II), auxin (IAA), and gibberellin (GA3) on abscission in explants of 14-day-old cotton (Gossypium hirsutum L.) seedlings were studied. Applications of Ab II, a potent accelerant (0.025 ,ug/abscission zone), resulted in a lysigenous breakdown of cells in a weakly defined separation layer in contrast to GA3, an accelerant (0.01 iig/abscission zone), and IAA, a retardant (0.125 ,g/abscission zone), which resulted in a schizogenous type of breakdown of cells in a well-defined separation layer, three or more rows of cells wide. Separation usually commenced adaxially with GA3, abaxially with IAA and in the controls, and either ad- or abaxially with Ab II. Cell division preceded abscission, the number of cells increasing greatly within 24 hr after GA3 treatment. Tyloses formed in vessel elements throughout the explant, both distal and proximal to the plane of separation in all treatments and in the controls. The retardant, IAA, appeared to stimulate tyloses formation. Tylosis development was not causal but was secondarily related to abscission. THE PHENOMENON of abscission, especially its induction, acceleration, and retardation by various endogenous and exogenous substances, has been investigated in many species, particularly in Coleus, Cossypium, and Phaseolus (Addicott and Lynch, 1955; Jacobs, 1962; Rubinstein and Leopold, 1964). The most frequent approach involved the effects of accelerants, retardants, and inhibitors of certain enzyme systems and key metabolic

The fine structure of blastocladiella emersonii zoospores

Abstract: A B S T R A C T The zoospore of Blastocladiella emersonii has been re-examined with the electron microscope. The following new findings were made. A double unit-membrane system surrounds all cell organelles except y-bodies, vacuoles and a few fragments of membranes. Lipid granules on one side of the large mitochondrion alternate with vesicles. The kinetosome of the posterior flagellum does not have any central fibrils as previously reported; a small, cylindrical structure is found within its anterior end. An associated centriole is located next to the kinetosome. Three striated rootlets pass from the kinetosome by separate channels through the mitochondrion. There appears to be no connection between the striated rootlets and the mitochondrion. Microtubules originating at the anterior end of the kinetosome pass into the cytoplasm between the mitochondrion and the nuclear cap. Long, dense strands were observed in some nuclei. The axoneme is taken up into the spore during encystment and is found in the freshly encysted spore. No trace of the flagellar sheath has been found in the encysted spore RECENTLY, three papers have appeared in

Morphogenesis of schizophyllum commune i. morphological variation and mating behavior of the thin mutation

Abstract: A single gene, recessive mutation of Schizophyllum commune, designated as thin, is characterized by its sparse growth on agar and unusual hyphal morphology. Many hyphae exhibit various degrees of "waviness," although some branches of these wavy hyphae appear normal. Differences in cell size and branch development betweeni normal and thin strains are also noted. Most of the characteristics attributed to thin vary quantitatively betweein strains. In addition, conisiderable variability in hyphal characteristics can be found in a single strain. Thin mutants behave as bilateral maters. In matings where the normal allele is present, genetic complementation occurs and normal clamped cells are produced. Fruit bodies with viable spores are formed on both the thin and normal sides of the mating. Thin X thin matings give a stable dikaryon, but they retain the thin morphology and do not produce fruit bodies. Evidence that there is only one locus for the thin mutation is presented. C'ertain aspects of the variability of thins, the possible role of extracellular polysaccharide, and the potential uses for thin strains in studies of hyphal and fruit body development are diseussed. SCHIZOPHYLLUM COMMUNE Fries is a tetrapolar basidiomyeete which has been used in numerous studies of the sexual mechanisms of the hymenomyeetes. A large number of different morphological mutations have been isolated and partially described from S. commune (Raper and Miles, 1958). One of these, the so-called thin mutation, differs from the other morphological mutants in that it is isolated with unusually high frequency from stock homokaryons (Raper, San Antonio, and Miles, 1958) and dikaryons (Miles, 1964). It is also commonly found in common-A heterokaryons as are a number of other mutants (Raper et al., 1958). The mutation was termed thin because of its sparse growth on agar. In addition, it displays a distinctive hyphal morphology generally described as "wavy" or "helical." It has been reported that the cells of thin are wider than those of normal strains and that fewer branches are found (Leary, 1964; Raper and Esser, 1964). Leary also reported that the cells of the thin strain which he studied did not vary significantly in length from normal strains. Raper and Esser reported that the cell length of thin is greater than that of normal cells. They also found that the mycelium of thin grew faster than the mycelium of normal strains. Leary obtained variable results on the relative growth 'Received for publication May 6, 1966. This investigation was supported in part by Research Gralnt A1-06570 from the National Institute of Allergy and Infectious Diseases of the U. S. Public Health Service and by Grant No. GB-3613 of the National Science Foundation. rates. In addition, Raper and Esser reported no difference in the angle of branching between thin and normal strains. The thin mutants show considerable potential usefulness in studies of hyphal development in regard to such aspects as the regulation of septum formation, branch initiation, hyphal structure and the role of extracellular polysaccharide, which Leary (1964) and others have reported as not produced by the thin mutants. The first part of this paper will deal with a more complete discussion of the morphology of the thin mutation. It has been reported that most of the morphological mnutations of S. commune, including thin, mate unilaterally (Raper and Miles, 1958; Leary, 1964). Unilateral maters donate nuclei to a compatible mycelium but do not allow the establishment of a dikaryon within their own hyphae. Raper and Miles (1958) found that by heavy seeding of a compatible thin X feather mating a few dikaryotic hyphae could be obtained. They coneluded that unilaterality appears to be caused by a failure of nuclear migration and not by a failure of formation of hyphal anastomoses. During a related study we discovered that the basic assumption that thin mutants are unilateral maters is incorrect; consequently, a more intensive investigation of the mating behavior of the thin mutants was undertaken, and the results of these studies are also reported here. MATERIALS AND METHODS-The 23 homokaryotic strains of S. commune used in this study

The cambium and seasonal development of the phloem in robinia pseudoacacia

Abstract: The cambium in black locust consists of several layers of cells at all times. Cambial reactivation (division) is preceded by a decrease in density of cambial cell protoplasts and cell wall thickening but not by cell enlargement. During the resumption of cambial activity, periclinal divisions occur throughout the cambial zone. Early divisions contribute largely to the phloem side. The period of greatest cambial activity coincides with early wood formation. Judged by numerous collections made during two seasons (October, 1960-October, 1962) the seasonal cycle of phloem development is as follows. Phloem differentiation begins in early April, ends in late September. The amount of phloem produced is quite variable (range: 1-10 bands of sieve elements per year). Cessation of function begins with the accumulation of definitive callose in the first-formed sieve elements and spreads to those more recently formed. By late November all but the last-formed sieve elements are collapsed. All sieve elements are collapsed by mid-winter and before the resumption of new phloem production in spring. Phloem differentiation precedes xylem differentiation by at least 1 week, and apparently functional sieve elements are present 3 weeks before new functional vessel elements. Xylem and phloem production ends simultaneously in most trees.

The spherosomes and the reserve fat in plant cells

Abstract: A B S T R A C T The deposition of reserve fat is studied in plants with a high, medium, or low lipid content, and is contrasted with the spherosomes of the same cells. In storage tissue with a high lipid content the reserve triglycerides have the form of comparatively large globules which are quite distinct from the spherosomes. In plants with a medium lipid content the reserve fat appears in the form of granules, globules, or oil-plasm, and as a homogeneous, interstitial deposition between the protein bodies. Plants with a low lipid content contain a very large number of spherosomes and only very few small sudanophil globules. The spherosomes and the reserve fat represent distinctly separate entities. THlS INVESTIGATION continues the study of the spherosomes and lipids which was originally carried out on the epidermal and guard cells of Cam panula persicifolia L. (Sorokin and Sorokin, 1966) and extends it to the vegetative and storage tissues of several plants. It was found in the earlier paper that the spherosomes contain phospholipids, are of uniform diameters, and have a limiting

The effect of ph on the uptake and accumulation of phosphate and sulfate ions by bean plants)

Abstract: A B S T R A C T Phosphate uptake above pH 6.0 followed the concentration of H-PO4. Sulfate studies were used to aid evaluation of phosphate data. Phosphate absorption was nearly linearly proportional to transpiration at pH 4.0; at pH 8.7, phosphate absorption occurred only early in the experiments. It was inferred that phosphate entered as H2PO4; that which entered at pH 8.7 did so as the result of a depressed pH at the absorption sites.

Auxin-Cytokinin Control of Secondary Vascular Tissue Formation in Isolated Roots of Raphanus

Abstract: A comparative study was made of the effectiveness of various horinoine anid metabolite mixtures in inducing vascular cambium initiation and secondary vascular tissue formation in isolated first-transfer oots of the radish, Raphanus sativus L. 'White Icicle,' when provided to the cut basal end of the root grown in sterile culture. An auxin, such as indoleacetic acid (IAA) at 10-5 M, a cytokinin, such as 6-benzylamino purine at 5 X 10M, a cyclitol, such as myo-inositol at 5 X 10-1 M and sucrose at 8% were all required for maximum response. Requirements for auxin and cytokinin were absolute; in their absence no cambium was formed. The addition of cyclitol, while not an absolute requirement for cambium initiation, increased the magnitude of the response markedly. Alternative auxins such as a-naphthaleneacetic acid and 2,4-dichlorophenoxyacetic acid were equally as effective as IAA. Alternative effective cytokinins included 6-furfurylaminlopurine, 6-phenylaminopurine and 6-(y,--dimethylallylaminio)purine. Alternative cyclitols equivalent to myo-inositol were seyllitol and pinitol. Other related cyclitols tested were much less effective or totally inactive. ISOLATED EXCISED ROOTS growIn in sterile nutrient culture usually do Inot form a vascular cambium or secondary vascular tissues. Only under unusual culture conditionis (Dormer and Street, 1948; Seeliger, 1956; Torrev, 1951) are secondary vascular tissues observed. Using a technique devised by Raggio and Raggio (1956) for culturing excised roots by providing organic nutrients via medium iintroduced into the cut basal enid of the root, Torrey (1963) was able to induce vascular cambium and limited secondary vascular tissue formation in excised roots of Pisum sativum L. Loomis and Torrey (1964) demonstrated with the same techniques that subcultured isolated I Received for publication 21 November 1966. This investigation was supported in part by research grant (GM-08145) and a special fellowship (no. 1F3GM2024-01) to RSL from the National Institutes of Health, U. S. Public Health Service. The technical assistance of Sharon Hosley and Pauline Borsari is gratefully acknowledged. roots of the radish, Raphanus sativus L., could be induced to form cambium and secondary vascular tissues bv introducinig appropriate metabolites and hormone mixtures through the cut basal end. They showed that, in additon to sugar in the form of sucrose, the excised radish roots must be provided an auxiin such as indoleacetic acid and a cytokinin, such as 6-beiizylaminopurine, both at appropriate low coincenitrations, in order to induce vascular camabium iniitiation. The addition of myo-iiiositol increased the response markedly. A further study has been made to determine the optimum coniditions in vitro for cambial initiation and for extenided vascular cambium activity in the excised radish root. A broad range of concentrations of the essenitial components, alone and in combinationi, was tested on first-transfer radish roots in. culture, and the ailatomical responses were determined in fixed and sectioned material. In the studies presenited below a comparisoin is made of ainatomiical responses observed October, 1967] TORREYl AND LOOM1-VASCULAR TISSUE FORMATION 1099 at the end of a period of approximately 4 weeks of treatment of roots subjected to a wide range of experimental conditions. Conclusions concerning the optimum concentrations of the chemical constituents required for cambial initiation and maintained activity are presented. Detailed considerations of the ontogenetic sequence in cambial initiation and secondary vascular tissue formation are presented elsewhere (Torrey and Loomis, in press). MATERIALS AND METHODS Ro0ots of radish, Raphanus sativus L. 'White Icicle,' were used in the anatomical studies described here. Mlethods of culturing and treating the excised roots have already been described in detail (Loomis and Torrey, 1964) and may be summarized briefly. Ten-mm root tips from 3-day-old seedlings germinated aseptically in sterile distilled water in the dark at 23 C were excised and cultured in a modified Bonner nutrient agar medium. After 4 days, when the isolated root tips were about 50 mm in length, 15-mm first-transfer tips were excised with a sharp scalpel and transferred to fresh nutrient medium in 11-cm petri dishes. The basal 5-mm portion of each root wtas inserted into a separate agar medium contained in a 12 X 35 mm glass vial. Ussually two roots were cultured in each 11-cm dish. The roots N-ere grown in the dark at 23 C for additional periods up to about 5 weeks. After various periods of culture, whole roots were removed, fixed in formalin-acetic acid-alcohol, dehydrated through an ethyl-butyl alcohol series, embedded in Tissuemat, and sectioned at 10 p. Sections were stained for anatomical study using Heidenhaiin's iron haematoxylin and safranin. From the studies reported earlier (Loomis and Torrey, 1964), it was know-n that aniatomical differences, especially with respect to the initiation of the vascular cambium and the development of secondary vascular tissuies, were dependent upon the preseince of hormones and hormone-like materials in the vial medium. Auxins, cytokinins, and cyclitols, as well as the concentration of sugar provided, appeared especially important. A large number of different combinations of nutrients both in the vial and in the plate medium had been tested for physiological response. Macroscopic observation of roots in culture usually showed whether secondary thickening of the roots had occurred, but it was necessary to make careful anatomical investigations in order to assess the extent and nature of the response to the various treatments. In the present study anatomical analyses were made of roots taken from approximately 64 different treatments. In the results described below, emphasis has been placed on the following aspects: the effects of auxin concentration including omission, auxin type; cytokinin concentration including omission, cytokinin type; cyclitol omission and type of cyclitol. A comparative study was made of structures formed in response to optimum concentration of these factors and to their absence from the vial medium. In making such an anatomical study large numbers of roots must be sampled and some variation in response is inevitable. Some arbitrary selection must be made of roots to be studied in this way. Usually each treatment involved 8-16 roots, but fewer than half of the roots wiere fixed and even fewer were selected for sectioning. Among those sectioned were the roots showing the maximum response as measured by root diameter. Despite this selection, the number of different reatments was sufficiently great so that a wide range of responses could be studied. The anatomical responses to similar treatments were remarkably consistent. Photographs of sections are selected as typical of the particular treatment and as showing good physiological response. In most cases any of a number of roots sectioned could have been used as illustrations. In the presence of optimum concentratioins of substances stimulatory to cambial activitv, the anatomical response was dramatic and a large root diameter resulted; in the absence of any one critical component, the response was markedly reduced or absent. IPhotographic comparison among roots from various treatments was made difficult, since useful magnifications varied markedly. In the accompanying photographs some compromise has been made in choice of magnification so that, where possible, cell detail can be seen. Large-diameter oots are reproduced to show overall response rather than cell detail. Some attention must be paid by the reader to the magnification of the photographs in comparing responses. In most instanices, the thickeening was macroscopically complete wN-ithin 14-21 days, but to be sure that all effects were observed the experiments were sometimes continued for longer periods. Some of the cambial derivatives continued to differentiate after cambial activity ceased, but the anatomical patterns in young (14-21 days) and old (28-35 days) roots were generally quite similar. The principal difference was that a cambial region of small, rapidly dividing cells was not as clearly evident in the old roots. The reasons for cessation of cambial activity constitute an important problem (Loomis and Torrey, 1964) w-hich is being investigated further. RESULTS As has been described briefly by Loomis and Torrey (1964), isolated 'White Icicle' radish roots in culture show maximum secondary vascular-tissue formation under the following cultural conditions. Plate medium: M\odified Bonner medium containing 2 % sucrose and vitamins (Bonner and Devirian, 1939). 1100 AMERICAN JOURNAL OF BOTANY [Vol. 54

Chromosome numbers in compositae. vi. senecioneae. ii

Abstract: Chromosome counts are reported for 76 taxa and 2 natural hybrids of tribe Senecioneae (Compositae). First counts are reported for several species of Senecioneae as well as for the genera Cadiscus and Whitneya. New chromosome numbers are added to those previously known in Arnica, Cacalia, and Seecio. Additional counts from Arnica support our previous suggestion that x = 19 for this genus. It is assumed that observed meiotic irregularities are associated with apomixis in this genus. Basic chromosome numbers for various New World sections of Seneco are proposed, and certain problems of sectional relationships in this genus are discussed. Chromosome numbers and plant morphology of Cadiscus, Hu8ea, and Whitneya indicate that these genera should be removed from Helenieae to Senecioneae. The possible affinity of the anomalous genus Adenocauon with Mutisieae is discussed. Data presented in the paper further support our earlier proposal that the basic chromosome number for Senecioneae is x = 10.