Showing papers in "American Journal of Botany in 1955"

Nutrition and growth of several blue-green algae

Abstract: LITTLE ATTENTION has been given to the more general features of the physiology of the blue-green algae. Specific attention has been given to nitrogen fixation (e.g., Allison et al., 1937; Burris and Wilson, 1946; Fogg, 1947) and limited aspects of photosynthesis (e.g., Emerson and Lewis, 1942; Frenkel et al., 1950; Duysens, 1952; Brown and Webster, 1953). Nutritional requirements have been investigated, notably by Fogg (1949), Gerloff et al. (1950, 1952) and Allen (1952). However, no study has been carried to the point of developing a blue-green alga as a reliable tool organism for physiological studies. There have been two obstacles to such development. One may be attributed to the difficulties of isolation and the lack of species in pure culture which suspend readily and submit to simplicity of manipulation possible with green algae such as Chlorella and Scenedesmus. A second difficulty arises from inadequate provision of carbon dioxide inherent in most of the culture methods used. Nutritional requirements have been defined in terms of the maximum growth yield obtained in cultures in cotton-stoppered flasks. Methods have not been developed for routine study of growth rate, a characteristic far more useful and interpretable for physiological work. The' present paper presents a development of culture media and methods which has led to description of the salient growth characteristics of three blue-green algae: Anabaena variabilis, Anacystis nidulans, and Nostoc muscorum G. Fragmentary data on three other blue-green algae are included. MATERIALS AND METHODS.-Because of the uncertainties of taxonomy of the simpler algae the species used will be described in terms of their history. 1. Anabaena variabilis (Kiitzing). Filamentous, but filaments very short in turbulent culture; isolated by and obtained from R. C. Hecker as Cylindrospermum sp. (1950); revised identification by E. G. Pringsheim. 2. Anacystis nidulans. Twoto four-cell filaments, but unicellular in turbulent culture; established as a unicellular culture by one of us (WK) and purified by M. B. Allen, tentative identification by F. Drouet; original description not found. 3. Nostoc muscorum G (Kiitzing). Filamentous, but filaments short in turbulent culture; obtained from G. C. Gerloff. 4. Nostoc muscorum A (Kiitzing). Filamentous, forming clumps even in turbulent culture; isolated by and obtained from F. E. Allison. 5. Anabaena cylindrica (Lemmerman) . Fila-

Gas exchange in the roots of mangroves

Abstract: ALONG THE southern and western coasts of the Florida peninsula occurs one of the greatest developments of mangrove swamp in the world. Rhizophora mangle L., the red mangrove, perching on its arched stilt roots, is the dominant species and the most marine. Another important component is Avicennia nitida Jacq., the black mangrove, which is restricted to the tidal zone and reaches its most luxuriant development on intertidal mud flats in more sheltered inland localities. Both species have a considerable tolerance for fresh water (Davis, 1943). Familiar to anyone who has visited the mangrove region are the air roots which protrude in great numbers from the mud under and around Avicennia bushes or trees. A single tree may produce several thousand of these air roots, usually 20-30 cm. high and a centimeter thick, soft and spongy, and studded with little whitish lenticels. In the mud they connect to radially-running main roots, which are also soft and spongy and contain large amounts of air (fig. 1). The vertical air-roots are often referred to as pneumatophores because it is believed that they may have the function of aerating the root system which lies buried in the mud. If one of the arching stilt roots of Rhizophora is dug out of the mud it is found to terminate in a bunch of long, spongy, finger-thick, and air-filled roots (fig. 2). The stilt root has a conspicuous development of lenticels, and one may wonder whether these might serve as ventilating ports for the mud roots. If they do, one might ask by what process the ventilation takes place, as it seems almost incredible that the voluminous roots down in the mud could be effectively ventilated by simple diffusion alone, through little lenticels high up on the stilt roots. One might also wonder how such a system, which gets its oxygen from the air, avoids getting jammed with nitrogen. However, before worrying over how the ventilation comes about one must first establish that such ventilation does take place, and this is the object of the present investigation. GAS EXCHANGE IN SUBMERGED ROOTS OF VARIOUS PLANTS.-Several investigators have analyzed the gases in roots of plants growing in water or mud which is poor in oxygen. In general these roots have been found to be aerated; how is usually not clear. Conway (1937), in a series of experiments on the sedge Cladium mariscus R. Br., found that air spaces were continuous from the leaves down into the roots. The gas connections were particularly free

The role of adventitious roots in recovery of shoots following flooding of the original root systems

Abstract: (1) Both original and adventitious roots flooded. 41% (2) Plants not possessing an adventitious root system were flooded to same depth as in treatment one _.._ . _..... 280/0 (3) Original root system flooded; adventitious roots not flooded _ __. __ .._. 71% flooded approximately one inch above the level of the adventitious root system, (2) normal plants were flooded to the same depth as those in treatment one, (3) the original root systems of plants possessing an adventitious root system were flooded, but the adventitious roots were not flooded, (4) normal plants were left in the cinder bench, and (5) plants possessing adventitious roots in addition to the original roots were left in the cinder bench. The plants without adventitious roots were dark green, stocky, and vigorous. The plants possessing adventitious roots were pale green, slender, and not as vigorous as those in the other group. The plants flooded above the adventitious root systems exhibited moderately severe epinasty within two days. The plants without adventitious roots, but flooded to the same depth, showed severe epinasty. There was little evidence of epinasty in those plants possessing adventitious root systems, but in which only the original roots were flooded. There was no evidence of epinasty in either group of control plants growing in the cinder bench. There was no further change for the duration of the experiment, eleven days. There was no significant difference among the three flooded treatments in degree of chlorosis of lower leaves or in number of new adventitious roots formed. The average growth-rate of the shoots for each treatment was determined during the first eleven days following flooding (table 1). The growth-rate of the normal control plants was 25 per cent higher than the growth-rate of the controls possessing an adventitious root system. The growthrate of the plants whose original roots were flooded, but whose adventitious roots were not flooded, was less than the growth-rate of the controls for one or more of the following reasons: (1) The effectiveness of the flooded original root system plus the unflooded adventitious root system was less than the root system of the controls, or (2) some factor or ONE OF THE primary problems in studies of flooding injury is the role of adventitious roots in recovery of shoots. Kramer (1951) noticed that recovery of shoots of Marglobe tomato and sunflower plants following flooding is coincident with the appearance of adventitious roots. Sartoris and Belcher (1949) found that those varieties of sugar cane which developed adventitious roots were less severely injured than those which did not develop them. Went (1943) contends that the root influence on shoot elongation is not due to the better known function of the root system, namely water and salt uptake, because no set of conditions insuring adequate water and salt supply of the cut shoot can replace the loss of the root system. He concluded that the roots which developed in moist air along the stem of plants whose root systems were submerged supplied one or more factors (tentatively named oaulocaline ) required for stem growth and prevention of chlorosis. Experiments were performed to answer the following specific questions as a basis for understanding the role of adventitious roots: (1) Is an adventitious root system, present at the time of flooding, sufficient to prevent injury to a shoot when the original root system is flooded? (2) Will removal of adventitious roots as they are formed prevent recovery of shoots whose root systems have been flooded? (3) Will removal of the adventitious roots plus sealing of the cut stumps with vaseline be more effective in preventing recovery of the shoots following flooding than mere removal alone? (4) Are roots, either original or adventitous, grown in water under conditions of comparatively good aeration \"physiologically adapted\" to conditions of poor aeration? METHODS AND RESULTs.-The role of adventitious Toot systems, present at time of flooding, in reducing injury to shoots of Marglobe tomato plants. This experiment was performed to determine whether an adventitious root system, present at time of flooding, is sufficient to prevent injury to a shoot when the original root system is flooded. Marglobe tomato plants approximately 45 em. tall, growing in pots of soil, were used as the experimental material. One group was set up so that adventitious roots developed along a section of the stem enclosed in a pint ice cream container filled with moist sand. An equal number of these potted plants was undisturbed. After adventitious root systems were established in the sand, the following treatments were initiated, utilizing five plants per treatment: (1) plants possessing adventitious roots were

In vitro studies on abnormal growth of prothalli of the bracken fern

Abstract: IN THE COURSE OF a study of prothalli of several species of ferns growing in sterile culture, it was observed that under these conditions there are frequent departures from the characteristic morphology. The occurrence of abnormal developments of fern prothalli in sterile culture has previously been reported on and extensively described by Hurel-Py (1950), Morel and Wetmore (1951), and others. Of all the species examined in this study, the bracken, Pteridium aquilinum (L.) Kuhn, showed the greatest variety and frequency of occurrence of abnormal developments. It was further found that certain of these abnormalities could be isolated and grown in separate culture where they manifested varying degrees of permanency.

Studies in the development of axillary buds

Abstract: IN MOST INVESTIGATIONS on the development of axillary buds, emphasis has been placed on the early stages of development with little attention being given to the later phases. As a result, there has been no clear concept of the timing and of the sequence of events in the growth of buds from their origin until maturity. It seemed desirable, therefore, that a series of investigations on the ontogeny of axillary buds be undertaken in several species of angiosperms. The first two papers of such a series described the origin and development of axillary buds in Syringa vulgaris L., Betula papyrifera Marsh. and Euptelea polyandra Sieb. et Zucc. (Garrison, 1949a, b). In this paper the progressive developmental stages of buds of seven other species are considered. The possible implication of the findings reported here to an understanding of the development and inhibition of buds and their use in horticultural practise will be discussed in a later paper.

The effect of ionizing radiation on plant growth

Abstract: The effects of high doses of radiation on plants is lethal, although different species of plants vary greatly in their sensitivity to ionizing radiation. There are reports, however, of a stimulating effect on growth when seeds or seedlings are exposed to light doses of ionizing radiation. Results of experiments conducted by the authors indicate that irradiation of seeds of various plants with 3000 r or X rays seemed to stimulate the growth of lettuce and cabbage, but more critical tests showed no significant effect of the irradiation. Irradiation of Gladiolus bulbs with 4000 r of X rays did results in significantly earlier flowering. 17 references, 2 tables.

Life cycle of ascosphaera apis (pericystis apis)

Abstract: THE FUNGUS under study, a common parasite of bee larvae in Europe, has gained recognition during the past thirty years as a transitional form between the phycomycetes and ascomycetes. It has been placed in the hemiascomycetes by different authors. One early investigator (Claussen, 1921) attempted to cross it with a mucor! Because of its uncertain systematic position and unusual cytological development, Professor Lindsay S. Olive of Columbia University suggested to the author that a restudy of the species with some of the newer techniques might prove enlightening. During this study, Dr. Donald P. Rogers of the New York Botanical Garden pointed out that the original generic name was not valid. Consequently, in a previous paper (Spiltoir and Olive, in press) the name Ascosphaera apis (Maassen ex Claussen) Olive and Spiltoir has been proposed. The reader is referred to this paper for a historical sketch of the subject and the proposed taxonomic treatment.

Levels of tissue differentiation in primary roots of pisum sativum

Abstract: ALTHOUGH THERE HAS BEEN a considerable amount of research on the problem of precisely where minerals and water enter roots, plant physiologists have not yet satisfactorily answered the vexing question. Many physiologists will agree that most attempts to obtain information pertaining to the place of entrance of minerals have, in reality, resulted in data relating to the place of their accumulation. In recent years some progress has been made in designing experimental methods that have yielded information, some of which appears to be contradictory, concerning the actual place of entrance of minerals and water (Hayward et al., 1942; Hayward and Spurr, 1943; Overstreet and Jacobson, 1946; Jacobson and Overstreet, 1947; Kramer and Wiebe, 1952). In connection with this problem, question of the role played by various root tissues in the movement of minerals and water centripetally through the root has been raised. Before the relative importance of each root tissue can be assessed, it is necessary to know precisely the spatial relationships of these tissues in roots growing in various environments. If it were found that the spatial relations differed in roots growing in different environments, a new experimental tool would be at hand. It could be used in designing experiments to give us more information regarding the relative influence of various root tissues on the entrance or rate of movement of minerals and water into and through roots. Heimsch (1951) called attention to the need for such data in his statement "if the range of differentiation and maturation of vascular tissues could be modified experimentally, it might be possible to identify the substances or conditions which control this aspect of growth and determine their specific influences." A great deal of speculation appears in both anatomical and physiological literature concerning the relationships of (1) the level of differentiation of one tissue to that of others and (2) the level at which a tissue differentiates (or matures) to the level at which certain physiological processes occur. Since we have relatively few data concerning the levels of tissue differentiation and maturation in roots, it seemed desirable to discover as many of these relationships as feasible for the roots of a particular plant. MATERIAL AND METHODS.-The common garden and commercial canning pea, Pisuim sativum, was

The leaf structure of poa annua with observations on its smog sensitivity in los angeles county

Abstract: Annual bluegrass (Poa annua L.) is very sensitive to certain phytotoxic agents present in smog and might be useful as a bioassay indicator plant. In the field, the characteristic response to hydrocarbon-oxidation products is seen to be a tan spotting or transverse banding limited to the region between tip and midblade of susceptible leaves. This damage has been duplicated in the laboratory with synthetically-produced smog. Tissue damage is similar to that previously described in spinach, beets, oats and other plants. The cells which are initially and most seriously damaged are those surrounding the substomatal chambers. Chloroplasts disintegrate, plasmolysis follows, and ultimate total dehydration of damaged cells results in part or all of the mesophyll tissue in affected areas becoming mummified. In plants having a high specific sensitivity to smog, damage is correlated with stomatal distribution and activity, volume of intercellular air space and age of cells. Localization of damage is related to the gradient of cellular differentiation from tip to base in the linear leaf; the sensitive region is limited to those cells which have just completed maximum expansion. 18 references.

Studies on abscission: the physiological basis of the abscission-speeding effect of intact leaves

Abstract: IN EARLIER PAPERS -in this series, the dominant role of auxin from a given leaf blade in controlling the normal rate of abscission of that petiole was demonstrated once again and the relation was quantified (Wetmore and Jacobs, 1953); it was further shown that the presence of intact, unfolded leaves resulted in faster abscission of nearby petioles which had been debladed (Rossetter and Jacobs, 1953). In general, the larger the number of intact, unfolded leaves and the closer they were to the debladed petiole, the faster was the abscission of the debladed petiole. The present paper reports experiments designed to elucidate the mechanism by which the presence of leaves speeds abscission of debladed petioles. A search through the literature brought to light no other reports of leaves speeding abscission of nearby organs. However, both auxin and ethylene, when artificially applied, have been reported to have activities such as might explain our observations. Minute amounts of artificially applied ethylene gas have been known for decades to induce rapid abscission of intact leaves (e.g., Doubt, 1917; Zimmerman et al., 1931). More recently, the production of ethylene gas by plant tissues has been demonstrated for a variety of detached and ripening fruits (Biale et al., 1954; review of earlier work in Biale, 1950). Hall (1951, 1952) stated that cotton and rose leaves which had been excised from the parent plants and placed for 4 days with their petioles in water "produced measurable amounts of ethylene." The "assay," however, was not as specific as the conclusion: it showed that some volatile substance could be collected which would reduce potassium permanganate. By the use of a more specific chemical test, ethylene production by excised leaves of Silybumn has recently been demonstrated (Pratt, 1954). Even before publication of this proof that at least some excised leaves can emit ethylene, Gawadi and Avery (1950) suggested that an "auxin-ethylene" balance might control abscission in the normal, intact plant-an idea taken up by Hall (1952) and Barlow (1952), although at that time there was no evidence that intact leaves produce ethylene or even have an abscission-speeding (and, therefore, ethylene-like) effect on each other. Addicott and Lynch (1951) reported an experi-

A new cretaceous conifer from northern alaska

Abstract: ONE OF THE results of the 1951 University of Michigan paleobotanical expedition to northem Alaska (Arnold, 1952) was the discovery of a new fossil member of the Taxodiaceae that is intermediate between Taxodium and Metasequoia. It represents a heretofore unknown genus for which the name Parataxodiwm is proposed. Its only species, P. wigginsii, is named in recognition of Dr. I. L. Wiggins, who, at the time of the expedition, was scientific director of the Arctic Research Laboratory at Point Barrow, and whose interest in the project contributed much to the success of the venture. The expedition, carried out during July and August of 1951, was for the purpose of exploring Naval Petroleum Reserve No. 4 for fossil plants. It was financed by the Office of Naval Research with the Arctic Research Laboratory supplying equipment and serving as the operational base. Because there are few named landmarks in that part of Alaska explored in 1951, the places where fossil plants were found are difficult to specify with precision. However, almost all maps of Alaska, even those of large scale, show a major bend in the Colville River about 75 miles south of the place where it flows into the Arctic Ocean. At this bend the river changes its course from an easterly one to almost due north. The new conifer was found about six miles downstream from this bend, on the right bank near the base of a high cliff. The locality is also three miles below the place where the Chandler River flows into the Colville and two miles upstream from the mouth of the Anaktuvuk River. Both of these tributaries, however, enter the Colville on the opposite side from where the plants were found. Positions of the lines of latitude and longitude differ as much as ten miles on different maps of the region under consideration, but on the Umiat map sheet of the Alaska Reconnaissance Topographic Series of the United States Geological Survey, Edition of 1952, the plant locality is in the vicinity of the place where parallel 690 30' north crosses meridian 1510 30' west. The high cliffs that flank the west bank of the Colville River extend for several miles both upstream and downstream from the plant localitv. At places they rise precipitously from the edge of the water to heights of 100 feet or more. Above the initial rise they may continue upward less steeply to still greater heights. The cliffs form a prominent headland in the angle of the bend mentioned above. Downstream for a few miles they trend away from the river channel but approach it again in the vicinity of the place where the plants were found.

On the development and structure of the cell wall in nitella

Abstract: THE INTERNODE CELLS of the aquatic alga Nitella axillaris Braun provide unusually interesting material for the study of cell wall development. In about two weeks these cylindrical cells grow from microscopic size to a mature length greater than 2 cm. The final diameter is about 0.3 mm. Throughout this growth the cylindrical surface of the cell is freely exposed to the aqueous medium; contact with the rest of the plant is made only at the ends of the internode cell (fig. 4). This report will present structural information about these walls and relate this information to other descriptive facts of wall development in Nitella. The growth pattern of the cell surface has been described (Green, 1954). If a longitudinal row of small evenly-spaced marks is placed on a young cell, the marks will be displaced by the growth of the cell. The marks become distant from each other in a way which demonstrates an essentially even distribution of elongation. Since the wall is at all times a right cylinder, increase in girth must also be evenly distributed along the cell axis. The row of marks, while maintaining its regularity, is transformed into a helical configuration as the wall elongates, hence a type of "spiral" growth is found in this cell. The twisted state of any cell may be quantitatively determined from an examination of the two striations which are representative lines of twist. The striations are visible in the living cell as colorless streaks in an otherwise uniform green layer of stationary chloroplasts just interior to the wall. These striations are 1800 apart on the cell surface and each forms a regular "Z-spiral" helix (the striation en the near surface of an upright cell being parallel to the diagonal of an upright letter Z). This helix is also termed "dextral." Each striation is almost parallel to the cell axis in the very young cell; the angle between a striation and the cell axis can become as great as 30? during the middle stages of development; the angle with the cell axis (/3) decreases to about 5? as maturity is reached. This normal development is diagrammed in fig. 4. Cells which cease to grow while in the highly twisted form maintain their twist permanently. Compressing or stretching such cells does not noticeably alter the twist. Further, growing walls in the twisted state show only a barely detectable

Further analysis of genetic control of heterocaryosis in neurospora crassa

Abstract: CONDITIONS FAVORING successful interaction, or the formation of a heterocaryon, between some biochemical mutant strains (Beadle and Coonradt, 1944) are known to be quite ineffective in others. This difference in response has been analyzed and found to be gene controlled (Holloway, 1953; Garnjobst, 19532). Because of the generally accepted view that heterocaryosis implies the compatibility of physiological reactions, further investigation is of considerable theoretical interest. Reactions of the two pairs of genes affecting heterocaryosis2 had not been experimentally examined in all possible combinations. These tests seemed desirable and have now been carried out. The results not only are consistent with the hypothesis that compatibility relations are concerned in heterocaryosis in Neurospora but they also suggest that certain genes may function in a rather specific way in determining compatibility. The two independently segregating genes described in a previous paper2 had been designated C (het-1) and D (het-2). The alleles preventing heterocaryosis, c and d, originally present in the inositol strain 37401 (inos) 3, were also found to be effective in preventing heterocaryon formation when either or both were genetically introduced into certain mutant strains originally of the CD genotype. The four possible heterocaryon genotypes CD, cD, Cd, and ed were obtained in the inos strain from a backcross of a CD inos isolate with the original strain. A riboflavin-requiring strain (Y30539, rib-2) of the CD genotype was used as a standard tester for the heterocaryon-forming ability of segregants of these crosses and of all subsequent interand intra-ascus crosses. All heterocaryon tests clearly proved that the presence of alleles C and D was necessary in both strains (inos isolate and rib-2 tester) to obtain a relatively stable heterocaryon (het+ phenotype). Other combinations (CD + cD, CD + Cd, and CD + cd) gave essentially negative (hetphenotype) results. The four heterocaryon genotypes have now been obtained from similar crosses in two other mutant strains the riboflavin tester strain and the nicotinicacid-tryptophan-requiring strain (39401, nt). All possible combinations of cultures having these genotypes, including those of the inos strain, have been tested for unisexual heterocaryon formation.

Development of the embryo sac in some american blackberries

Abstract: APOMIXIS WAS FOUND in northeastern American polyploid blackberries during the course of breeding experiments conducted by Einset (1951). Twenty-four species and clonal varieties of blackberries (subgenus Eubatus, basic chromosome number 7) with somatic chromosome numbers ranging from 21 to 63 were selfed, open-pollinated, or crossed with a blackberry plant having a different chromosome number. Pollination was essential for seed set in every case. IChromosome counts showed that 80100 per cent of the seedlings of 21-, 35-, 49or 63chromosome seed parents possessed the same chromosome number as the female parent, whether it had been selfor open-pollinated or crossed with a male parent of a different chromosome number. When 28-chromosome seed parents were crossed with odd-ploid pollen parents 80 per cent of the seedlings were tetraploid. These seedlings were assumed to have developed from unfertilized, unreduced eggs. Seedlings having more than the somatic chromosome number of the female parent made up 0-7 per cent of the total progenies of the seed parents of each level of ploidy. Most of these were considered to have arisen from fertilized, unreduced eggs. Twenty-eight-chromosome seed parents produced 14-chromosome offspring totalling 6.3 per cent of the progenies, indicating that a reduced egg could develop parthenogenetically. Many aneuploid seedlings of polyploid seed parents conceivably originated from the union of reduced eggs and sperm, one or both having an aneuploid chromosome number. Seedlings resulting from the development of fertilized reduced eggs undoubtedly composed part of the tetraploid progeny of open-pollinated 28-chromosome seed parents, but could not be detected by somatic chromosome counts. The present paper will describe the development of the embryo sac in a diploid species of blackberry which reproduced sexually (Einset, unpublished data) and in six polyploid species which behaved pseudogamously (Einset, 1951). The terminology used will be that of Maheshwari (1950). MATERIALS AND METHODS.-Embryological material was collected from Rubus allegheniensis Porter (2x), R. canadensis L. (3x), R. localis Bailey (3x), R. beltobatus Bailey (Kittatinny) (4x), R. abactus Bailey (5x), R. meracus Bailey (7x), and R. flagellaris Willd. (9x). Rubus allegheniensis was growing wild in a hedgerow in Geneva, N. Y. The rest of the material was gathered from either the same plants or vegetative propagations of the same plants in the collections of the New York State

Influence of sulfur on the toxicity of selenium to Aspergillus

Abstract: Experiments were performed to investigate the influence of the sulfur/selenium ratio and sulfur amino acids on the selenate inhibition of Aspergillus niger. All the sulfur amino acids investigated were able to counteract, partially or wholly, the inhibition of growth. Mycelial growth and selenium accumulation were found to be a function of the sulfur/selenium ratio when sulfur was supplied as sulfate and selenium as selenate. As the ratio was increased, growth increased and selenium accumulation decreased. The results suggest that selenate toxicity in this organism is of a multiple nature, consisting of a number of competitive actions between sulfur and selenium analogues. 34 references, 4 figures, 3 tables.

Relation of chlorosis to concentration of iron in citrus leaves

Abstract: SEVERAL INVE$TIGATORS have adopted the concept that iron chlorosis is caused by physiological unavailability of iron in the tissues. The evidence presented here indicates that this concept is not valid, at least as far as citrus is concerned, anid that iron chlorosis involhes a simple deficiency of iron in the leaf. Visible symuptoms of iron chlorosis (lime-induced chlorosis) in citrus leaves are similar to those found in many other crop plants, namely, green veins sharply distinguished from a less g,reeni or yellow mesophyll. These symptoms are attributed to improper iron nutrition on the basis of the following evidence: (1) the leaf pattern can sometinies be cured by applying iron to the soil or other nutrient medium; and (2) affected leaves usually respond witl increased greenness to surface application of iron solutions, but such response does not result from applications of other nutrient elements (see discussion bv Jljin, 1952). Nutrient deficiencies are generallv accompanied by low concentrations of the deficient elements' in certain plant organs, particularly leaves (Goodall and Gregory, 1947)Although some investigators have reported this situation with iron in lime-induced chlorosis (e.g., Gile and Carrero, 1920; Menchikowsky and Puffeles, 1935), many have failed to find consistent differences in iron concentrations in chlorotic and healthy leaves (Ilj in. 1952 McGeorge, 1949; Wallace. 1928) . From this situation came the idea that not all the iron in chlorotic leaves is metabolically active; supportling evidence was supplied by Oserkowsky (1933!who showed that iron extracted from leaves by 0.3 N HCI correlated well with chlorophyll content. The conc.ept of physiological unavailabilitv of iron still appears to be prevalent (Leeper, 1952) in spite of the demonstration by Jacobson (1945) that. after thorouglh removal of surface contamination from the fresh leaves of some deciduous fruit trees, total iron content correlated well with chlorophyll content. The work of Smith et al. (1950), in Florida, indicates that this correjation probably holds also in citrus leaves. Their studies support the conclusion of Jacobson that iron-contaminants such