Apr., 19391 GUSTAFSON-AUXIN IN FRUITS 189 outside and at many stages during the developmen­ the cessation of division in successive tissues; and tal period from very small ovary primordia to ma­ (c) greater cell expansion after cell division ceases. ture fruit. Differences in fruit size are therefore usually due In each tissue growth takes place at first chiefly to differences in both cell number and cell size, by cell multiplication, though cell size slowly in­ though either factor may alone be responsible in cer­ creases also, After a specific cell size is reached, di­ tain cases. vision ceases, and all further growth of this tissue is Specific differences in development between Cu­ hy cell expansion. curbiia and the three other genera are described. The innermost tissues, as compared with the suc­ Possible factors responsible for the differences in cessively outer ones, show (a) more rapid increase cell division and in cell expansion between the vari­ in cell size during the period of cell division, (b) ous tissues and in the various races are discussed. earlier cessation of division, and (c) greater cell The problem of the size relation of cell to organ size at the time when division ceases. is part of the more general problem of the factors In Cucurbita Pepo, large-fruited races as com­ determining growth and differentiation. The first pared with small-fruited ones typically show (a) no step in the solution of this problem is a thorough difference in cell size during early development; (b) descriptive analysis in quantitative terms. a more extended period of cell division, due to less DEPART~IENT or BOTANY, rapid increase in cell size, greater cell size at the COLUMDlA UNIVERSITY, time of last division, and a greater interval between NEW YORK CITY

LITERATURE CITED .:bIELUNG, E. 1893. t;ber mittlere Zellengrossen. Flora MACARTHUR, J. W., AND L. BUTI.ER. 1938. Size inherit­ 77: 176-207. ance and geometric growth processes in the tomato HrXLEY, J., AND G. TEIssn:R. 1936. Terminology of rela­ fruit. Genetics 23: 253-268. tive g-rowth. Nature 137: 780. SACHS, J. 1893. t;ber einige Beziehungen der specifischen Grs'rAFsoN, F. G. 1939. Auxin distribution in fruits. Grosse der Pflanzen zu ihrer Organisation. Flora Amer. Jour. Bot. 26: 189-194. 77: 49-81. HOUGHTALING, HELEN B. 1935. A developmental analysis SINNO'lvr, E. 'V. 1930. The morphogenetic relationships of size and shape in tomato fruits. Bull. Torrey Bot. between cell and organ in the petiole of A eel'. Bull. Club 62: 243-252. Torrey Bot. Club 57: 1-20.

AUXIN DISTRIBUTION IN FRUITS AND ITS SIGNIFICANCE IN

FRUIT DEVELOPMENT 1

Fclix G. Gustafson

GnoWTH SUBSTANCES or auxins, as they will be in many plants. In this paper it was shown that the called in this paper (Went and Thimann, 1937), are auxin content is actually much higher in the ovaries now generally considered to be factors in vegetative of those plants that produce fruits parthenocarpi­ growth of plants. Recent investigations on artificial cally than in similar varieties requiring fertilization parthenocarpy produced by chemicals (Gustafson, for fruit production. 19:36; Hagemann, 1937; Gardner and Marth, 1937) Before it is possible to proceed very far with this have shown that auxin under artificial conditions matter, it is first necessary to investigate the auxin can also cause fruit development without fertiliza­ distribution in fruits. In 1936 Dollfus published tion. This coupled with the fact that auxin has been some experiments which tended to show that auxin shown to be widely distributed in the vegetative is produced in the developing seeds. He used the parts of plants leads one to assume that auxin is diffusion method. In these experiments he found also concerned with normal fruit growth. Gustafson that a substance diffused from the ovules into the ( 1939) has proposed the theory that a high auxin agar which caused Avena coleoptiles to curve, but content in the ovary in the flower bud stage is re­ no such substance diffused out of the outer part of sponsible for natural parthenocarpy, which is found the ovary. Meyer (1936) has also found auxin in

1 Received for publication December 15, 1938. fruits. He extracted the auxin with alcohol in a Paper from the Department of Botany of the Univer­ reflux condenser for two hours and mixed the ex­ sity of Michigan, No. 682. tract from 10 grams of fresh material with 1 gram The writer wishes to express his thanks and apprecia­ tion to F. W. 'Vent, E. G. Anderson, J. Van Overbeek, of lanolin, which was applied to one side of intact and William S. Stewart, of the California Institute of Avena coleoptiles. While this method is perhaps not 'I'echnology, and to William Hertrich of the Huntington so good as the method in which agar containing the Gardens, San Marino, California, for various aids ex­ auxin is applied to decapitated etiolated Avena tended during the course of this investigation and to the Directors of the Horace H. Rackham Trust Fund of the coleoptiles, nevertheless it is fairly accurate. In University of Michigan for financial aid. these experiments Meyer used a number of species 190 AMERICAN JOURNAL OF BOTANY [Vol. 26.

of plants, and in the fruits of all these species he was A few experiments were performed in which the able to demonstrate the presence of auxin. He did plant material was placed on the agar blocks as in not do much with the distribution within the fruits, Went's original experiments. In most instances such but in the few determinations he made, seed material blocks when placed on Avena coleoptiles caused no gave a greater Avena coleoptile curvature than the curvatures. It had been hoped that this method could other parts of the fruit. be used, but as so few plants gave any results, it was The present work was undertaken to investigate abandoned for the extraction method. This brings further the auxin distribution in fruits. Fruits from up a question which is in the minds of many­ many plants, in different stages of development and namely: Is extracted auxin the same as that which during different seasons, were used. diffuses into the agar block, and if so, is the con­ PROCEDURE.-The work here reported was done centration in the plants that give negative results so at the William G. Kerckhoff Laboratories at the low that only by using a large quantity of material California Institute of Technology. Part of the ex­ can a test be obtained; or is the auxin which is ob­ perimental material was grown especially either in tained by extraction released from a combined form, the greenhouse or in the field, while some of it, as with low diffusibility, by the extraction treatment? the Yucca Whipplei, Agave Brundigii, Pittosporum Those experiments in which, by daily extraction, ac­ undulatum, and Clivia sp., was obtained from the tive material continued to be obtained for a period Huntington Gardens at San Marino. The auxin con­ of 10 days certainly suggest an affirmative answer to tent and distribution was determined hv the Avena the latter alternative. method, the technique of which has be~n discussed In these experiments the fruits were separated in detail by Went and Thimann (1937). into an interior and exterior part, or, as in the to­ Auxin was extracted with freshly distilled ether mato and summer squash, further subdivisions were according to Van Overbeck's (1938) modification made. When a fruit was divided into only two parts, of other methods. Th~dried residue was thoroughly the interior part included the central axis, the pla­ mixed with a known amount (usually .4 to .8 cc.) of centae, the ovules and all the cells in between and 1.5 per cent agar and after standing 90 minutes was immediately surrounding the ovules, and the exte­ poured into a nickel plated brass mold 1.5 X 8.0 X rior part usually included only the ovary wall, as in 10.5 mm, in size. After the agar had been cut level the peppers, tomatoes, beans, and Yucca. In the sec­ with the surface of the mold, the large block was cut ond experiment with peppers, listed in table 1, the into 12 equal pieces. The material was now ready beans and Yucca, only the ovules and seeds were in­ for the test. Great care was taken to have freshly cluded in the interior part. The extraction method prepared extracts. Usually the extract was pre­ varied considerably in these experiments. All mate­ pared the same day that it was used, but if the ex­ rial was cut into rather small pieces to begin with, tract could not be used the same day that it was but in some experiments these pieces were frozen made, it was always stored in a refrigerator in dried with liquid air, and while they were in the frozen condition. Fleshy material was repeatedly extracted condition, attempts at maceration were made. These until the Avena test plants showed no curvatures differences in treatment of the material should in no when treated with the agar-extract. In some experi­ way influence the results, as all material experi­ ments such material as tomato and squash was first mented with at anv one time was alwavs treated in frozen with liquid air then ground in a mortar and the same way, anl extractions were co~tinued until the ether added. The extraction was always carried no further reaction was obtained with the Avena out in the dark and usually, though not always, at a coleoptiles. low temperature. The investigation was divided into two parts. Control experiments in which Avena plants were Part one dealt with the auxin distribution in non­ treated with a known concentration of indole acetic parthenocarpic fruits, and the second part with a acid (usually 21.5 gamma per liter) were run with comparison of auxin concentration in artificial par­ every experiment. (This concentration ordinarily thenocarpic and non-parthenocarpic fruits. In the gave a curvature of about 10-12°.) By this means second part the same plants were used, and the ex­ the sensitivity of the test plants was determined for tractions were of course made at the same time. each experiment, which was very important, because RESULTS AND DISCUSSION.-Distribution of au.rin there was considerable variation day by day, and iciihin non-parthenocarpic fruits.-In determining the auxin concentration in a plant can be calculated the auxin distribution within fruits, a number of dif­ in terms of indole acetic acid (see Van Overbeck) ferent plants were used, and the experiments ex­ rather than in terms of some of the many units which tended over a period of five months from :\1arch to have been employed by different investigators. This August. The differences in auxin contents that have procedure has the advantage that the activity of the been noted in different experiments with the same growth substance or substances is recorded in terms species of plants are probably partly due to sea­ of a known and easily obtainable substance, indole sonal differences and partly to difference in the acetic acid. One does not know what the substance is vigor of the plants. The tomatoes in table 1, the nor is its concentration known, but it is known that first experiment with peppers in table 1, and all the its activity on a decapitated Avena coleoptile is equal peppers in table 5 were grown in the greenhouse to a known concentration of indole acetic acid. during the winter or early summer, and the plants Apr., 19391 GUSTAFSON-AUXIN IN FRUITS 191

TAIII.E 1. Aua,in distribution within fruits. The interior From the information gained in these experiments include.• only ovules 01' seeds in Yucca, beans, and Yucca in which only seeds or ovules were used. In the second experiment wUh pl!ppers,. otherwise it in­ it seems as if the se~ds or developing seeds must be clu des till! central axis, the placentae, ovules, and all centers of auxin production. This is particularly in­ cells in between or clo.•ely a.•.sociated. w,ith them. Fig­ ures denote anxin concentration in terms of indole dicated by the experiments with peppers, beans, and acetic acid equivalents in gammas per kiloqram. green the other fruits other cells adjoining the seeds were weight, exrept in the diffu.•ion experiment with Pit­ used, and the results are not so positive for them. tosporum. The second experiment with pepper.•, the To clear up this point, crookneck summer squash experiments with cucu-mbers, crookneck summer and tomatoes were used in several experiments in «quashee, and beans toere made durin.'! the summC1', which the seeds were separated from the rest of the and the others during the zointer 01' spring. fruit, which was further subdivided.

Weight Weight TAIlU: 2. Auxin di«tl·ibution in [ruit.• of tomato and of mate- of mate- rrookneck «ummer .•qua.•h. AnJ,in concentration is rial, in rial, in denoted. in terms of indole acetic acid equivalent, and Plant Interior grams Outside grams the figul·I!.. denote gamma.. pC1' kiloqram of [re..h material. Theee experiments tcere made during the Pepper (first experi- H'llnl,mfJ,'J". ment) . 0.16 31.7 0.07 156.2 Pepper (second ex- Neek of periment) . 61.90 3.95 2.'29 6·kO Tissue squash Tomato . 0.06 91.40 0.0'2 276.60 Plant and condi­ Seeds around Ovary without Agave Brundlqil . 0.:27 :31.0 0.06 85.0 tion of fruit or ovules ovules wall seeds Cucumber . 5.06 95.7 1.99 81.0 Crookneck summer Squash, yellow, 40 squash em. long, wt. Buds . 14.09 7.3'2 7..5'2 1:2.66 77'2.:2 g ...... 1.31 3.38 0.48 o.rs Flowers . 7.30 16.4'2 1.21 21.50 Tomato, green, 4--5 Young fruits . 0.58 31L5" 0.00 12t.15 em. 0 ••••• • •••• 10.60 2.15 0.36 Kentucky wonder bean Pods 7-10 em . 108.80 2.19 3.24 64.1 In two experiments tomato fruits were separated Pods 1:2-14 em . 20.89 8.55 1.41 152.5 into five parts and these parts extracted separately. Pods about 19 em. 7.00 33.66 0.46 73.1 Included in one of these experiments were parthe­ Yucca Whippll!i nocarpic fruits produced by phenylacetic acid. Phe­ Fruits 1.8X2.7 em. 0.34 19.51. 0.1'2 42.05 nylacetic acid is known to give practically no Avena Fruits '2.3X3.4 em. 0.67 2'2.28 0.13 38.04. Fruits 2.5X3.5 em. 0.23 26.H 0.12 40.58 test, and therefore fruits were produced by its stimu­ Pittosporum utulula­ lation to determine whether these parthenocarpic tum (diffusion) '24 fruits make or at least contain auxin. Table 3 gives Aoena coleoptiles the result of these experiments. used . 0.00 These experiments show that the ovules or young '- seeds are high in auxin content and that the other were not particularly vigorous, while the second ex- parts of the fruits contain much less auxin. Whether periment with peppers employed fruits grown in this auxin is produced in the ovules or diffuses into the field, where the plants were much more vigor- them from the leaves, we have no way of knowing ous. The fruits were also larger. Even though there from these experimcnts. Nevertheless, the results was considerable difference between different lots as a whole indicate that growth (however initiated) of fruits, the relative concentrations within the fruits sets up a concentration gradient with the highest were much the same in all experiments with the concentration in the ovules, when present, otherwise same fruit. The auxin concentration was much lower in the central axis and partition region and with a in the winter and spring than in the summer. low concentration in the ovary wall.

TAII!.E 3. Auxin di.•trilmtion in tomato fruits, produced by pollination and parthenocarpicallu by by phenylacetic acid. The fruits were green and between 4.5 and 6.0 cm. in diameter. A u

Jelly Central around seeds axis and Type of fruit Seeds or ovules Placentae partitions Periearp

Normal (Exp. 57) ...... 15.33 6.57 9,44 2.27 1.'27 Normal (Exp. 65) ...... 30.03 0.45 2.47 9.69 0.63 Parthenoearpic (Exp. 65) ...... 1.25 M9 6.42 0.81 192 AMERICAN JOURNAL OF BOTANY [Vol. 26.

Comparison of auxin content in parthenocarpic a single spraying. It is not clear whether this means and normal fruits.-In the preceding section it has that a greater percentage of flowers on a branch been shown that the ovules or seeds of fruits have produced fruits or whether a larger number of a high auxin content. In order to answer some of the treated flowers produced fruits. From the sentence questions which have been raised concerning the following their statement that several treatments growth of fruits, it is necessary to know whether or are more efficacious than a single one, it seems that not there is auxin production or accumulation in they have reference to the whole branch. "In the fruits when no seeds are produced. practical use of these compounds in producing fruit It is a well-known fact that in certain interspecific on holly, successive spraying would be necessary crosses or even in intergeneric crosses, the ovary in that the blossoms are not all open at one time." may develop into a fruit without any seeds. Accord­ Several injections of auxin into ovaries and fruits ing to Yasuda (1935) the pollen tubes bring into the of tobacco produced no more growth than a single ovary something which stimulates growth. This is injection, according to Gustafson (1938a). If Gard­ undoubtedly auxin (Gustafson, 1937). The auxin ner and Marth's statement has reference to a cluster brought into the ovary is certainly not sufficient to of holly flowers as a whole, it would seem that the cause continued growth, and the query has been added auxin merely initiates the growth and that made as to where this additional growth substance the ovary either produces or obtains from the leaves enough for its continued growth and that if this TABLE 4. Comparison between auxin concentration in nor- mal and parthenocarpic tomato fruit s, Aux:n con­ source is not sufficient for the needs, the fruit stops cent ration is denoted in term.• of indole acetic acid growing. equivalent, and the fi.gures indicate gammas per kilo­ To obtain information on this point, tomato fruits gram fresh weight. were produced parthenocarpically by means of phe­ nylacetic acid. Phenylacetic acid, as mentioned be­ Pollinated Parthenocarpic fore, has only a very slight influence on the Avena Condition of fruit Pericarp Interior Pericarp Interior test. The auxin determination was made in the usual way. Table 3 shows one of these experiments, and Green, 3.0 X in table 10 are found two more determinations on 4.0 cm. diam ... 4.00 ;n.O~1 0.40 0.7:2 Green, 4.6 X such fruits.

6.5 em. 0 •••••• g.57 7.53 0.73 g.06 Parthenocarpic fruits produced by naphthalene acetic and indole butyric acids were also used, and table 5 gives the results for peppers. These fruits comes from. Another variation of the above ques­ were grown in the greenhouse, during the spring and tion has been concerned with the growth of nor­ early summer. mal parthenocarpic fruits as oranges, lemons, and According to "Yent and Thimann (1937), indole grapes. Where does the auxin come from that causes butyric and naphthalene acetic acids produce slight them to grow? There is probably no pollination and curvatures in Avena coleoptiles so that we have no no development of seeds. In artificial parthenocarpy information about the naturally occurring auxin in produced by chemicals, interest has centered around these experiments, but they definitely demonstrate the continuation 01' non-continuation of growth in a that there are growth promoting substances in the fruit after the initial stimulation. Gustafson (1937, growing fruits to which the Avena is sensitive; 1938a, 1938b) has reported a number of instances in whether these are the substances added at the time which the initial growth stopped very soon, whereas of flowering or natural growth hormones, we do not at other times a fruit continued to grow until half size and then stopped; in still other fruits growth know. The concentration of this active substance is continued until maturity. What is the cause of this lower than in normal fruits, however. difference in behavior? Is the auxin supplied to the In the experiments with fruits produced by phe­ ovary in the form of paste or spray causing all of nylacetic acid there is no doubt that parthenocarpic the growth during the enlargement of the fruit, or tomatoes contain naturally occurring auxin. If auxin does the developing fruit itself supply a part? occurs in tomatoes, one would expect it to be pres­ Gardner and Marth (1937) found that four spray­ ent also in other fruits. Whether this auxin is pro­ ings produced a larger percentage of setting than duced in the fruit or conducted into it from other

TABLE 5. Comparison between auxin content in normal and parthenocar-plc peppers. Amount of material used is denoted in .grams inside the brackets. Auxin concentration is denoted in terms of indole acetic acid equivalent.•, and the figures indicate gammas per kilogram of fresh material.

Normal fruits Parthenocarpic whole fruit Seeds and placentae Pericarp Naphthalene ac, Indole butyric

0.16 (31.7) 0.07 (156.g) 0.07 (1l4.0) 0..53(15.0) 0.80 (16.6) 0.1 (100.0) 0.g5 (49.5) 0.18 (51.0) 1939] Apr., GUSTAFSON-AUXIN IN FRUITS 193 sources, we do not know, and it need be of no con­ Some may hesitate to accept the idea of auxin cern. That it is there is the main point. playing such an important role in the growth of It then seems very likely that in some fruits there fruits. Let these consider that fruits have artificially is a quantity of auxin sufficient for the needs of con­ been started and caused to develop by the addition tinued growth, after growth has once been initiated, of auxin. If auxin is able to do this when added from even though no seeds are produced, while in others the outside, is there any reason why it should not the amount is too low for the needs of a continued play an important part under normal conditions? growth, and development ceases after some time. Furthermore, let it also be remembered that the In varieties where mature parthenocarpic fruits mere pollination without fertilization does some­ have never been obtained, it is likely that the natu­ times cause fruits to develop, and auxin has been rally occurring auxin content is always too low to extracted from pollen (Laibach, 1932; Thimann, sustain growth after the artificial supply has been 193·1,), and Gustafson (1937) extracted a substance depleted, and the only way such fruits can be made which, when placed on the pistil of a flower, caused to grow and mature is by continuously supplying it to develop into a fruit. All these experiments show them somehow with auxin as do the seeds in non­ that there is auxin in the pollen and that it may parthenocarpic fruits, but we have not yet discov­ cause growth of fruits. ered a method of successfully doing this. In spite of these statements it is to be under­ In normal fruits in which pollination and fer­ stood that auxin is not considered to be the only fac­ tilization are necessary we can consider it a reason­ tor involved in fruit growth. In a recent publication able hypothesis that the initiation of growth of the Went (1938) considers that auxin acts in such a ovary into a fruit results from the auxin brought way as to cause other substances which he calls into it by the pollen tubes. If this is true, then one calines to move to the part of the plant where might expect that right after pollination the auxin growth takes place. Thus he considers that auxin content should be higher than just before. Meyer re­ causes the caulocaline to move to the apex of a stem ports" that just after fertilization, which might have where it functions in the growth of the stem. The reference to pollination, the auxin concentration in auxin may then be thought of as a master reagent the female flowers of Cucurbiia Pepo, Cucumis sa­ causing other substances to produce growth of one tivus, and Helianihus annuus was much higher than sort or another. If this idea is applied to the growth just before fertilization, and he also makes the gen­ of fruits, it becomes obvious that auxin causes some eral statement that there is less growth hormone in other substance or substances to move into the ovary female flowers before fertilization than afterwards. of a flower and there cause growth to take place. it In the present investigation there is little if any evi­ is not necessary at the present time to have a name dence that there is more auxin after pollination than for such a hypothetical substance, but by analogy it before. In fact, it would be very difficult to get such would be carpocaline, if different from other forma­ information when much material is needed for ex­ tive substances. traction. Even if it could not actuallv be shown that the auxin content was higher after pollination, that SUMMARY is no serious criticism of the hypothesis, because even a little auxin added in the right place, as the The auxin content of ovules and developing seeds ovules, would be sufficient to cause them to grow and is much greater than that of other parts of fruits, set up auxin centers from which auxin might diffuse and it is considered possible, even though not yet into the ovary. In a preceding paper (Gustafson, proved, that they produce auxin. 1939), it was shown that in two-week-old Paper Auxin other than that added artificially is found rind and Valencia seeded oranges the auxin content in fruits that have been produced by treating the had increased very much over that in the flower flower by phenylacetic acid. stage. After the embryo has commenced growing, The probable role of auxin in the growth of par­ auxin in considerable quantity is present in the seed. thenocarpic and non-parthenocarpic fruit is dis­ This auxin undoubtedly diffuses into other parts of cussed. the ovary, where growth takes place. Even if seeds DEPAR'nIENT OF BOTANY, are not produced, there is auxin present in the UNIVERSITY OF MICHIGAN, ovary. AXN ARBOR, MICIlIGAN

LITERATURE CITED Dor.I.FUS, H. 1936. Wuchsstoffstudlcn. Planta 95: 1-'21. 1938a. Further studies on artificial partheno­ GARnNI:R, F. E., ANn P. C. MAIITII. 1937. Parthenocarpic carpy. Amer. Jour. Bot. 95: 937-'244. fruits induced hy spraying with growth-promoting 1938h. Induced pa rthenocarpy, Bot. Gaz. 99: compounds. Bot. Gaz. 99: 184-195. 840-844. GUSTAI'SON, F. G. 1936. Inducement of fruit develop­ 1939. The cause of natural parthenocarpy. ment by growth-promoting chemicals. Proc. Nat. Arner. Jour. Bot. :26: 135-138. Acad. Sci. g:2: 6.'28-63(i. HAGEl\IANN, P. 1937. "Cher durch B-indolessigsaure ---. 1937. Parthenocarpy induced by pollen extracts. ausgeliiste Parthenokarpie del' Gladiole. Gartenbau­ Amer, Jour. Bot. 94: 10'2-107. wissenschaft. 11: 144-150. 194 AMERICAN JOURNAL OF BOTANY [Vol. 26.

LAIBACH, F. 193,.). Pollenhormon und Wuchsstoff. Bel'. WENT, F. W. 1938. Specific factors other than auxin Deutsch. Bot. Ges. 50: 383-390. affecting growth and root formation. Plant Physiol. MEYER, F. 1936. tiber die Verteilung des Wuchsstoffes in 13: 55-80. del' Pflanzen wahrend ihrer Entwicklung. Disserta­ ---, AND K. V. THDIAXN. 1937. Phytohormones. tion. Johann \Volfgang Goethe Universitiit zur New York. Frankfort am Mainz. YASUDA, S., T. INABA, AND Y. TAKAHASHI. 1935. Par­ THDIAXN, K. V. 1934. Studies on the growth hormone of plants. VI. The distribution of the growth sub­ thenocarpy caused by the stimulation of pollination stance in plant tissues. .Jour. Gen. Physiol. 18: 23-34. in some plants of the cucurbitaceae. (Japanese with VAN O"ERBEEK, J. 1938. A simplified method for auxin English resume.) Agriculture and Horticulture 10: extraction. Proc. Nat. Acad. Sci. 24: 4;?-46. 1385-1390.

OBSERVATIONS ON THE GENUS PSEUDOLPIDIUM 1

D. A. McLarty

FOLLOWING THE early observations of Nageli erence to this striking similarity between the zoospo­ (1846), several workers, including Cienkowski rangia and resting-spores but in all cases describes (1855), Braun (1855), and Pringsheim (1860), re­ and figures spherical, definitely thick-walled, spiny ported the presence of various bodies in swollen resting spores which differ from the Olpidiopsis type filaments of water molds; but little intense work was of spore only in the absence of the adjacent cells. done on them until Cornu (1872) published the re­ In swollen filaments of Achlya secured in Novem­ sults of his studies. He recognized these bodies to ber, 1937, conspicuous, cylindrical, smooth sporan­ be parasites and described several species, in three gia (fig. 10) were observed together with long, spiny of which he observed spiny, thick walled resting sporangia (fig. 11) as described by Fischer for P. spores with one or more smooth or slightly echinu­ fusiforrne. In the same culture smooth, ellipsoidal lated, thin-walled, empty cells attached to them. zoosporangia (fig. 14) were present as well as spiny Cornu considered these spores to have arisen from sporangia of the same size and shape (fig. 15), a fusion of a smaller male thallus with a larger fe­ which have been described by Fischer for P. Sapro­ male one and interpreted the empty cells as the an­ legniae. Dependent apparently upon conditions of theridia. Using this sexual spore character as the growth, zoosporangia were found to vary greatly in diagnostic feature, Cornu thus established the genus size and shape, and in any culture a complete series Olpidiopsis for these small, intramatrical parasites. from spherical to cylindrical could be observed. Later Fischer (1880), studying what he thought Spiny sporangia showed similar variation in size to be Cornu's type species O. Saprolegniae, failed and shape, and the degree of spininess was found to find resting spores with attached antheridial cells to vary from slight echinulations to heavy bristles. and came to doubt Cornu's earlier observations. In These bristly bodies showed no tendency to rest but 1882 he rejected the "adjacent cell character" and liberated zoospores readily, thereby proving them­ restricted the genus Olpidiopsis to forms which pos­ selves to be nothing more than zoosporangia which, sessed asexual resting spores. Subsequent studies, however, convinced Fischer that his earlier work was incorrect, and in 1892 he confirmed the ob­ servations of Cornu and reinstated the genus Ol­ pidiopsis to its original status. At the same time, he established the genus Pseudolpidiurn to include Ol­ pidiopsis-like species which produce resting spores without adjacent cells. Of the six species which Fischer recognized, only two are tenable, inasmuch as he did not observe the resting spores of four of them. In P. Saprolegniae he described smooth, flat­ spherical to ellipsoidal zoosporangia (fig. 5, 6) and spiny resting spores of similar size and shape (fig. 9). In P. fusiforme Fischer described smooth, long ellipsoidal to cylindrical zoosporangia associated with similar long, spiny resting spores (fig. 2). Fig. 1-9 were copied from plates given by Fischer and Butler (1907), studying various other species of Pringsheim.-Fif.!'. 1-2. Stages in the development of the Pseudolpidiurn, has not supported Fischer with ref- resting-spore of Pseudolpidium [usiforme (127X, after Fischer).-Fig. 3-5. Stages in the development of the I Received for publication January 14, 1939. zoosporangium of Pseudolpidium Saproleqniae (B7 X, The writer wishes to express appreciation and thanks after Fischer).-Fig. 6. Zoosporangia of Pseudolpidium to Prof. H. B. Berdan, of the University of Western Ontario, for the culture from which this study was made, Saprolegniae (87X, after Pringsheim).-Fig. 7-9. Stages and to Prof. .J. S. Karling, under whose direction this in­ in the development of the resting-spore of Peeiulolpid.am vestigation has been carried on, for his help and criticism. Saprolequiae (1l7X, after Fischer).