Showing papers in "American Journal of Botany in 1956"

Cytogenetics and evolution of the grass family

Abstract: DURING THE past half century that part of botany, and in fact all biological science, which deals with evolution and classification has entered a new era, dominated by the rise of cytology and genetics, and their use 'as new tools for solving evolutionary and taxonomic problems. This union of disciplines has yielded striking results, and the new relationships uncovered by it have often been supported by data from still other fields, such as anatomy, embryology and physiology. Thus plant evoluionists are gradually progressing toward their avowed goal; the understanding of the complex interrelationships between and the evolutionary origin of the myriad diverse types of plants existing on the earth, and the establishment of general principles which have governed this evolution. No --group of plants has been more radically affected by this new approach than the grass family. There are several reasons for this.' In the first place, grasses are very important to us. They feed our cattle, sheep, and other livestock. A few species of the family, the cereal grains, have become our staple foods, while another, sugar cane, sweetens our lives. If we are home owners, we cut the grass every week so that we can enjoy the soft turf and cool green expanse of our lawns; and while resting we often pluck its leaves or stems, admire their structure, or teach our youngsters how to turn a grass leaf into a shrill whistle by placing it between our thumbs. If we live in a dry climate and hike over the hills in summer, we come home to spend hours plucking the seeds of the weedy or "stickery" grasses out of our clothing or our dog's hair. In many parts of the world one group of grasses, the bamboos, are the staple building material for houses and bridges. Because of these many uses, the study of grass classification or taxonomy does more than satisfy our curiosity about the diversity of living things and the way in which they have evolved. Cereal and sugar cane breeders have learned that many species of wild grasses are closely enough related to the cultivated crop species so that hybrids between them can be obtained. By back crosses or introgression from such hybrids, the gene pool available to the cereal or cane breeder can be enlarged to include extra genes for vigor, disease resistance, and such valuable qualities as high protein content of the grain. Breeders of forage grasses are trying out interspecific hybrids as a means of obtaining greater vigor, as well as resistance to drought, cold, or unfavorable soil conditions. Specialists in lawn and turf management find that an understanding of grass taxonomy is most helpful to their work. For all of these purposes, the most useful system of classification is one which reflects as nearly as possible the true genetic and evolutionary relationships of the species concerned. A second reason for the changing grass taxonomy is that grasses are difficult for the taxonomist. In the words of Edgar Anderson, they are "streamlined." Their leaves are all alike in shape, and their stems vary relatively little in branching pattern. Their flowers are so reduced that the calyx and corolla, though probably present in the form of small scales (palea and lodicules), are very hard to study, and their ovary is reduced to a simple. 1-seeded caryopsis. An amateur in systematic botany who has not tried to recognize the genera and species of grasses could visualize the plight of the grass taxonomist if he should try to place into genera and species a large number of specimens of, say, the rose family which had been mutilated by cutting off all of the flowers at the summit of their pedicels, and trimming the leaves down to a narrow ribbon. If he did this, he would find his attention becoming focussed on the inflorescence, particularly the pattern of its branching, and the shape of the reduced leaves or bracts which subtend the branches. These are exactly the characters which grass taxonomists have traditionally emphasized. The near revolution which is now taking place in grass taxonomy began when a few anatomists like Grob, Duval-Jouve, and Pee-Laby began to examine and compare the leaves of grasses under the microscope. They found that the smooth surface of the grass epidermis, so plain to the naked eye, appears under the microscope as a mosaic of highly distinctive cells; siliceous cells, parenchyma cells, hairs of various types, and specialized cells surrounding the stomata. An equal diversity of cells and tissues can be seen on examining a grass leaf in cross section. Furthermore, these cell patterns are characteristic of a species, and often diagnostic also of genera and tribes. But when grasses are classified on the basis of these anatomical characteristics, the arrangement of genera which emerges differs strongly from the classical system based upon characteristics of the inflorescence. It is perhaps for this reason that grass taxonomists paid little attention to these anatomical studies. But in 1931 there appeared the first important work on the cytology of grasses, the monumental treatise of the Russian cytologist Avdulov. He found that if one classifies grasses on the basis of the number and size of their chromosomes, one forms a system strikingly similar to that based on anatomy and histology, and equally different from that founded on the traditional characteristics of the inflores-

Morphological evidence concerning the origin of the b genome in wheat

Abstract: THE CULTIVATED hexaploid wheat is an allopolyploid with three distinct genomic complements, A, B, and D. Of these, D was contributed by Aegilops squarrosa, as shown by Kihara (1944), and McFadden and Sears (1946). Though the correspondence of the A genome of the tetraploid emmers (AB) with the A of the diploid einkorns (A) is not perfect (Kihara and Lilienfeld, 1932), wheat cytologists generally assume that the tetraploids and therefore the hexaploids receive their A genome from the einkorn group (Sears, 1948). There is also general agreement concerning the close relationship of the two emmer genomes with the A and B of the hexaploids. This leaves the B genome as a distinct unit, the origin of which is still unknown. Various workers have attempted to identify the parental species that contributed the B genome to tetraploid wheat by means of cytological studies of its hybrids with other species, but these attempts have been unsuccessful. The main cause of these failures has been ascribed to the great antiquity of the tetraploid wheat and hence the many changes that must have occurred in the B genome since its incorporation into the allotetraploid (Sears, 1948). Following Kihara's classical work on Triticum and Aegilops, the usual practice of genome analysis has been the use of diploid species with known genomes as analysers, for the determination of the genomic complement of related allopolyploids with more than one genome, on the basis of meiotic pairing (Lilienfeld, 1951). However, meiotic pairing can hardly be recognized as an indication of the complete genetic homology of two genomes, since partially homologous chromosomes often pair readily and form chiasmata, especially in many groups of grasses which contain closely related species. Obviously the method of genome analysis does not fully justify the assumption that genomes denoted by identical symbols are really identical in their gene content or in the structural pattern of their chromosomes. Further, genome analysis is possible only when the diploid parents in question are known and serves to verify their identity. Thus, in order to discover an unknown parent involved in the phylogeny of an allopolyploid, the method of genome analysis can be used only by a process of trial and error. Since chromosome pairing in the hybrids between tetraploid wheat and its supposed diploid relatives has not clarified the relationship of the B genome, we must

Some factors for tuberization in the potato plant

Abstract: LITTLE IS KNOWN about the factors which determine tuber formation in the potato and in other tuberous plants. Most of the work with potatoes has dealt with the finding of conditions under which the plant produces its maximum yield, breeding new varieties for yield and disease resistance, and with studies dealing with the tuber itself. Several authors (Dostal, 1945; Deusse, 1947) have postulated the existence of a specific, hormone-like, transmissible factor for tuberization. Doposzheg-Uhlar (1911) attempted the isolation of a substance of the above nature from Gloxinia, but without conclusive results. On the other hand, others have suggested that tuber formation is a matter of surplus carbohydrates formed by the potato plant. (Driver and Hawkes, 1943; Arthur et al., 1930.) Bernard (1902) attempted to show that tuberization is brought about by the symbiotic relationships of the plant and a fungus. At present this fungal theory has not been entirely discarded.

The effect of light intensity on rate of apparent photosynthesis in leaves of sun and shade plants

Abstract: THE RELATIONSHIP between photosynthesis and light intensity has been a subject of investigation by plant physiologists for a great many years. A number of light curves of photosynthesis are presented by Rabinowitch (1951) in his discussion of the light factor. Most of these curves however are for the lower plants. Of the approximately two dozen curves presented only 5 are for higher plants. Data are presented in tables for compensation points of various species but here again the lower plants far outnumber the higher plants. With the exception of the table on maximum yield of photosynthesis under natural conditions it is apparent that most of the available data on compensation point and saturation light intensities are for the algae. That the number of light curves of photosynthesis of higher plants is limited is evidenced by the few citations presented by Thomas (1955). Most of these which he does discuss are for plants growing under field conditions. Information relative to compensation points, saturation light intensities, and maximum photosynthesis at norlnal atmospheric CO2 concentration of a number of species of plants is available in the literature. The diversity of experimental conditions under which these data were obtained, however, makes difficult the comparison of rates of photosynthesis of different species of plants. One can not always be sure whether the differences are inherent differences of individual plants or differences which result from variations in experimental procedure. It was the purpose of this investigation therefore to obtain data relative to compensation points, light saturation and maximum photosynthetic rates of several species of plants under similar experimental conditions. Species of plants from two physiological groups were chosen. Those which could be classed as typical sun plants and those classed as typical shade plants. The experimental procedure was designed such that the exposures to the various light intensities during the actual measurements of photosynthesis would be of short duration so that in the case of shade plants solarization might not occur. MATERIALS AND METHODS.-The apparatus used to follow the course of photosynthesis consisted of a tank of compressed air to provide a uniform concentration of C02, a Plexiglas leaf chamber (fig. 1) in which could be inserted an attached leaf or frond as in the case of fern, a column of Drierite to

Studies on roots. iii. an analysis of root growth in phleum pratense using photomicrographic records

Abstract: THE GROWING ROOT TIP has long been considered a favorable object for experiments on growth and differentiation. In contrast to the shoot it has a relatively simple structure, unencumbered with foliar and floral appendages. The literature on this subject has been well reviewed in the recent papers of Erickson and Sax (1956a, 1956b). In 1939 Sinnott pointed out the suitability for growth studies of the roots produced by certain species of small-seeded grasses. The transparency of the fine roots and the rudimentary character of the root cap permit unobscured microscopic observation of the surface of the living meristem. Investigations on the growth of one of these species, Phleum pratense L., were reported by Sinnott and Bloch (1939a) and by Brumfield (1942).

Visual indications of s35 and p32 translocation in the phloem

Abstract: EVIDENCE THAT the phloem is the path of movement of minerals, food substances, and other materials such as vitamins, auxins and viruses in plants has been obtained bv a number of methods (Crafts, 1951). Among the visual methods has been the use of dyes, lithium salts and other substances. Mechanical methods include the separation of the wood and the bark or killing of certain stem areas by steam. Among the metabolic methods are the tracing of sugar from leaves to other areas as reflected by growth and the use of 2,4-D or other growth substances as evidenced by stem curvature. None of these methods, except possibly the first, isolates the exact path of movement. The use of radioactive tracers has introduced new refinements of techniaue which have greatly facilitated translocation studies. Although there has been no visual proof of the exact path of movement the evidence has indicated that the phloem tissue is involved. The present work is an attempt to refine this technique to include a visual method for locating the exact path of movement. MATERIALS AND METHODS.-Red Kidney bean plants were grown in a one-half strength Hoagland solution under controlled conditions of temperature. humidity, and light; namely 23? ? P?C., 60 ? 2.5 per cent relative humidity and fluorescent lighting yielding 1000 to 1200 f.-c. The plants were used twelve days after the hypocotyl straightened, when the oldest trifoliate leaf was fully matured, the second was well expanded and the third just un1folding. Two methods were used for introducing the P32 and the S35 into the plant: first, by introducing the tracer into a vein of the leaf which was severed and a flap cut so that the initial movement was toward the periphery of the leaf and from there through intact veins into the petiole and the stem (Biddulph, 1941); and second, by spraving the tracer onto the underside of the terminal leaflet of the first trifoliate leaf. Twentv-five M1. of solution were used for iniection and fifty PI. for spraying. The pH of the radioactive phosphate and sulfate solutions was approximately 6.0 and the amount of radioactivitv varied between 100 and 720 ec per treatment. The migration period of the radioactive solution veried from one hr. to one hr. and 20 min. depending upon the amount of mobile p32 which was detected in the stem of the plant by the use of a G-M tube with a window thickness of 1.4 mg./cm.2 which was attached to a portable scaler and recording circuit.

Genetics of sordaria fimicola. i. ascospore color mutants

Abstract: SORDARIA FIMICOLA is a homothallic pyrenomycete which, like 8-spored species of Neurospora, produces asci, each with eight dark ascospores in a single orderly series. No other type of spore is produced by this species. Recently the writer (1954) obtained a gray-spored mutant by means of ultraviolet irradiation. When the mutant culture was paired with a wild-type culture, some perithecia were produced which contained asci with four wild-type and four gray ascospores, thus making possible a direct analysis of segregation of the spore color locus in the ascus. Zickler (1934) studied a similar phenomenon in the asci of the heterothallic pyrenomycete Bombardia lunata, and Bistis and Olive (1954) reported on the segregation of two different loci affecting spore color in the heterothallic discomycete Ascobolus stercorarz us.

Seed dormancy in rosa as a function of climate

Abstract: THE SEEDS of many plants are known to be dormant at maturity, and to require a period of exposure to low temperature to enable them to germinate under subsequent suitable conditions. In Rosa, and in several other rosaceous genera, this lowtemperature after-ripening is widely regarded as a fixed and characteristic prerequisite to further development of the embryonic plant. Joseph (1929) pointed out that rosaceous seeds require low temperature stratification to prepare them for germination. Haut (1938) found that apple, cherry, peach and pear seeds must be after-ripened before germination will occur. Crocker (1927) reported that seeds of temperate-zone roses germinate well only following a period at low temperature, and Crocker and Barton (1931) determined the after-ripening requirements of hybrid and species rose seeds, as well as those of several other rosaceous seeds. The ubiquitous nature of the low-temperature after-ripening requirement of rosaceous seeds is apparently unquestioned in recent literature, with the exception of a report by Calvino (1930) stating that hybrid rose seeds grown at San Remo, Italy, germinated readily with no prior low-temperature treatment. This report was accorded little significance, and the results were logically explained by Crocker and Barton (1931) by supposing that the seed were inadvertently exposed to winter temperatures sufficiently low and prolonged to allow afterripening to occur. More recently, however, there have been unpublished reports from southern France, and from some of the inland valleys of California, claiming successful germination of hybrid rose seed without resort to low-temperature treatment. These reports have been partially substantiated in this laboratory by the collection or import of seed from several localities, and in the course of the investigation it has become apparent that the dormancy of hybrid rose seed of a given genetic origin may vary widely from year to year, and from one region to another. The present paper deals with the quantitative aspect of the dormancy, and with the relationship between the dormancy and the pre-harvest climatic environment. MATERIALS AND METHODS.Temperature data were obtained in the experimental field from shielded maximum and minimum registering thermometers. Sunlight data were calculated from the Local Climatological Data of the U. S. Weather Bureau station at Portland, Oregon. This station is

Studies on the growth and inhibition of isolated plant parts. v. the effects of cobalt and other metals

Abstract: ALTHOUGH COBALT has never been proved to be essential for higher plants3, nevertheless it strongly promotes the growth of certain isolated plant parts. This remarkable fact was first reported by Miller in 1951, and later (Miller, 1954) it was shown that the effect on pea stem sections is much increased by the presence of sucrose. Meanwhile, brief mention had been made that the effect had been confirmed (Thimann, 1951), though no promotion was observed in Avena coleoptile sections, and it was shown also that cobalt increases curvature in the slit pea stem test (Thimann and Marre, 1954). Recently, also, cobalt has been found to promote growth of tissue cultures of pea epicotyls (Howell and Skoog, 1955), and to improve spore germination in one of the rusts (Turel, 1955). It had earlier been shown to inhibit cell division and stimulate the production of mycelial forms in yeast (Nickerson and van Rij, 1949). The purpose of the present paper is to give details of the results previously reported and of others obtained later, to compare the responses of different plants and the action of different metals, and to examine possible explanations of the phenomenon. In the course of this work Avena coleoptiles have been found to respond satisfactorily to cobalt, but only at concentrations very much lower than for peas. Although many of the experiments were made 3 or 4 years ago a recent resumption of the work has ensured that all observations have been repeated, while the earlier ones have been extended and amplified. MATERIALS AND METHODS.-Straight growth tests were carried out on both Avena coleoptile sections (10 mm. long) and Pisum stem sections (20 mm. l6ng) and curvature tests on the latter as described before (see Thimann and Bonner, 1948; Thimann and Marre, 1954; Thimann, 1951). Growth took place at 25?C. in the dark. Solutions were adjusted to pH 5.5 at the start, but no buffer was added except where specified in the text. Every buffer introduces special ion effects which influence growth favorably or otherwise. Avena sections excrete acid during growth, usually reaching about pH 4.2 in 24 hr. and 3.6 in 72 hr.; the quantity of acid is such that M/1000 buffer does not hold the pH at

Crossing over in chlamydomonas reinhardi

Abstract: THE UNICELLULAR green alga Chlamydomonas has been used for genetic investigations by several workers who have studied the inheritance of sexuality (Moewus, 1938; Smith and Regnery, 1950; Lewin, 1953), and the production and the inheritance of several types of morphological and physio-logical mutant strains (Lewin, 1952, 1953; Nybom, 1953; Sager, 1954, 1955; Eversole and Tatum, 1956; Eversole, 1956). The most extensive contribution to the present knowledge of Chlamydoomonas genetics has been made by Moewus. One of the most interesting results of his work was the finding that during meiosis crossing over in C. eugametos occurred at the four-strand stage at room temperature but only at the two-strand stage at temperatures below 5?C. (Moewus, 1938). Since these results are of considerable theoretical interest as to the mechanism of crossing over, investigations were begun in an effort to determine whether crossing over at the two-strand stage could be detected in another species, C. reinhardi. The studies reported here involve the recovery of genetically useful mutant strains, the establishment of linked markers, and the analysis of tetrads to distinguish between crossing over at the twoand at the four-strand stage. MATERIALS AND METHODS.-Tlaploid (+) and (-) cultures of C. reinhardi (strain 137C) obtained from G. M. Smith were used for this investigation [mating type (+) and (-) is enclosed in parentheses in order to avoid confusion with + which is used to designate the wild-type alleles of mutant genes]. Stocks were maintained in pure culture on agar slants and were grown at 26?C. under daylight fluorescent lamps at a constant light intensity of 150 f.-c. The life cycle of C. reinhardi has been described recently by Sager (1955). Media.-A mineral nutrient medium composed of 10 per cent Beijerinck's solution (Bold, 1942), 2 per cent agar, and M/150 phosphate buffer (pH 6.8-7.0) in distilled water supports growth of both the (+) and (-) wild-type strains of C. reinhardi in the light. This minimal medium was used throughout except where otherwise indicated. Detection of mutants and types of mutant strains obtained.-After ultraviolet irradiation of vegetative cells mutant strains were recovered by means of the layering method of Lederberg and Tatum (1946) or the surface irradiation technique of Wyckoff (1930). The supplemented medium used with both of these techniques was prepared by the

Sexuality in ascobolus stercorarius. i. morphology of the ascogonium; plasmogamy; evidence for a sexual hormonal mechanism

Abstract: DURING A recent genetic study (Bistis, 1956) of Ascobolus stercorarius (Bull.) Schr6t. it became apparent that any attempt to interpret certain of the genetic data would require a more detailed account of the life cycle, particularly the stages of the sexual process up to and including plasmogamy. This species is heterothallic (Dowding, 1931; Bistis, 1956); consequently each ascus fusion nucleus must be, heterozygous for the compatibility factors. Since mutation at the mating-type locus has never been observed, ascogonia produced by single ascospore cultures are presumed to -be homocaryotic. In matings, plasmogamy, which brings together the complementary nuclei, is of the gamete-gametangial type; there are no antheridia. Although there is a considerable literature on the morphology of the ascogonium, the nature of the fertilizing element was correctly determined only by Miss Dowding. She reported that the transfer of oidia of one mating-type onto a mycelium of a compatible strain results in the development of fertile apothecia. Possibly here, as in several other heterothallic ascomycetes lacking an antheridium, the fertilizing element may be any cell containing nuclei of opposite mating-type. A detailed account of the sexual process up to and including plasmogamy is presented in this paper. In addition, evidence for hormonal control of certain stages in this process will be given. MATERIALS AND METHODS.-The-cultures used in this investigation were single-ascospore isolates obtained through the courtesy of Dr. Clare Yu and Mrs. Jane Rhein. The medium used for vegetative culture consisted of yeast extract (0.4 per cent), glucose (1.0 per cent), and Difco Bacto-agar (2.5 per cent). For the production of fruiting bodies the medium (Yu, 1954) consisted of yeast extract (0.025 to 0.3 per cent), cellulose (a disk of 9 cm. Whatman No. 7 filter paper in each dish), and Difco Bacto-agar (2.5 per cent). The method devised for studying the interaction of oidia and mycelium has these basic steps: (1) an inoculum taken from a three-day-old culture of the a mating-type isolate (ascogonial parent) is placed at the center of a 9-cm. dish containing 25 cc. of the yeast extract-cellulose medium, (2) three days later a small block of fresh yeast-extract agar

An anatomist's view of virus diseases

Abstract: ANATOMIC STUDIES of plants affected with viral diseases have taught us much about the behavior of viruses in their host plants and, at the same time, have added to our store of information on reactions of plant cells and tissues to internal injuries. Interest in the anatomy of plants having disorders induced by diseases and other agencies may be traced back to the early days of anatomical research. This parallel development of the inquiries into the normal and the abnormal structures is only natural, for plants are constantly exposed to agents and conditions that interfere with their development. In fact, our usual division into normal and abnormal structures is rather arbitrary. When we say "normal" we simply mean that something is true in the majority of instances. Some would object even to this broad definition of normal since, actually, the peculiar changes in diseased and otherwise disturbed plants are normal reactions to the inj urious or merely modifying effects. The difficulty of defining normality is further compounded by the fact that whatever criteria we may choose for distinguishing between normal and abnormal, be it with reference to structures or to reactions, the normal and the abnormal intergrade with one another so that a clear delimitation between the two is not to be found. We need terms and categories, however; for recording our observations and for conveying their meaning to others. The important thing is not the term or category itself, but that the sense in which they are used be made perfectly clear. For the present purpose we may agree that normal is something we have chosen-somewhat arbitrarily, to be sure-to set up as a norm; with reference to plants, this norm may be a structure or activity usually encountered in plants that grow in conditions most appropriate for them, free of diseases or other disturbances. The opposite is abnormal, that is, something that deviates from that which we established as a norm. Considering the history of the anatomy of disturbed or deranged plants, the so-called pathological anatomy, we find that pertinent information was compiled in 1909 by Sorauer, then, more comprehensively, in 1925 by Kiister, both German botanists. Kiister's work was a milestone in that it not only assembled the information in orderly fashion but also crystallized the terminology with regard to the pathological anatomy of plants. There is, as a result, a rather general agreement on such terms as hypertrophy and hyperplasia, referring to phenomena of abnormally intensified growth and differentiation, and hypoplasia, denoting inhibition of growth and differentiation. Commonly hypertrophy is used to designate an excessive enlarge. ment of a cell or a part of it; hyperplasia, an excessive mutliplication of cells. In contrast, we use only one term, hypoplasia, to denote inhibition of development, be it expressed in too small a size of cells or cell parts, or too small a number of cells or cell parts, or nondevelopment of some features that are normally expected to be present in the cell or tissue at the particular stage of their development. Death of cells and tissues is referred to as necrosis, with necrotic as the, adjectival form. A review in the English language of some of the general aspects of pathological anatomy-or morbid anatomy, as the author called it-was written by Butler in 1930. He paid particular attention to the fungal and bacterial diseases. Otherwise the information on the anatomic effects of fungi and bacteria must be sought in various compendia and special articles dealing with the diseases induced by these causal agents. A considerable volume of literature in pathological anatomy deals with the very interesting and highly complex plant galls, mainly those induced by insect stimulation. Viruses were recognized later than fungi and bacteria as causal agents of plant diseases, and the first comprehensive review on the structural effects of the viruses upon plants appeared in 1938 (Esau, 1938). Workers of various countries have studied virus diseases and, incidentally, described the internal symptoms, but mostly those in plants in which the disease had become well established. The ontogenetic, or developmental, approach to the studies of the anatomy of virus-diseased plants and the extensive inquiry into the biologic relation between viruses and the tissues of the host are developments that resulted in a large measure from work in the United States (see Bennett, 1940b, 1956; Esau, 1938, 1948b).

The form and function of numeral patterns in flowers

Abstract: SOME OF the basic structural designs in the various flower types are the numeral combinations of flower parts. Regular forms of di-, tri-, tetra-, penta-, hexa-, octo-, deca-, dodeca-, and polymerous symmetry make flowers look clearly different even when they have the same color and size (fig. 1). For certain plant groups, definite numbers of flower parts are so distinctive that taxonomists readily use them as constant characteristics for identification of species, genera, and frequently even larger taxonomic units. Besides, these symmetrical figures of flowers have undoubtedly played an important role in the development of human art and architecture. The cardinal figures of trefoils, quatrefoils, cinquefoils, sixfoils, dixfoils, etc. in numerous folk ornaments, and particularly in Gothic architecture, are very close imitations of the above listed numeral combinations of flowers and of plant leaves.

Arachis hypogaea. normal megasporogenesis and syngamy with occasional single fertilization

Abstract: EXTERNALLY NORMAL FRUITS which are empty or contain only shriveled seeds occur frequently in the cultivated peanut, Arachis hypogaea L. These seed failures are caused by an unfavorable environment (calcium deficiency) or by an unfavorable genetic constitution (interspecific hybridization). An explanation in developmental terms of the observed sterility in this geocarpic plant is of both agronomic and botanic interest. To provide a factual basis for such an interpretation it first was necessary to examine the reproductive mechanism of the species for possible irregularity and to determine whether empty fruits could arise by parthenocarpy. This paper presents the result, a description of the life history of Arachis hypogaea from ovule initiation to syngamy. MATERIAL AND METHODS.-Flower buds and very young fruits were collected from plants of the Virginia and Spanish varieties, grown under field conditions at Raleigh, N. C. There were no important differences between the varieties in the phases of development considered. Fertilization stages were obtained by tagging individual flowers at anthesis and collecting at 2-hr. intervals during the succeeding 40 hr. Karpechenko's fixative was used with an aspirator; sections were cut at 10-15 g and stained in Heidenhain's haematoxylin or in Delafield's and safranin. Best results followed bleaching in one per cent potassium permanganate (Johansen, 1940). Plasmolysis was troublesome only in mature embryo sacs. OBSERVATIONS.-The ovule. Early stages of carpel and ovule development (fig. 1-3) occur in buds 1-3-mm. long in which the anthers already have a well differentiated archesporium. The apical ovule arises first (fig. 2) from the ventral margin of the carpel, and appears before the carpel is completely closed. The basal ovule arises immediately below the apical one (fig. 3). The two ovules (occasionally three), which occur in the Virginia and Spanish varieties, are inserted alternately along the ventral suture (fig. 14). One-ovulate carpels are rare. The primary archesporial cell is probably hypodermal, but is not distinguishable from the adjacent meristematic cells of the nucellar apex. When it first appears, the single megasporocyte is in the subhypodermal cell-layer and is associated with one