Butler University Botanical Studies
Volume 7 Article 4
The ts em smuts of Stipa and Oryzopsis in North America George W. Fischer
Follow this and additional works at: http://digitalcommons.butler.edu/botanical The utleB r University Botanical Studies journal was published by the Botany Department of Butler University, Indianapolis, Indiana, from 1929 to 1964. The cs ientific ourj nal featured original papers primarily on plant ecology, taxonomy, and microbiology.
Recommended Citation Fischer, George W. (1945) "The ts em smuts of Stipa and Oryzopsis in North America," Butler University Botanical Studies: Vol. 7, Article 4. Available at: http://digitalcommons.butler.edu/botanical/vol7/iss1/4
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Butler University Botanical Studies (1929-1964)
Edited by
Ray C. Friesner
The Butler University Botanical Studies journal was published by the Botany Department of Butler University, Indianapolis, Indiana, from 1929 to 1964. The scientific journal featured original papers primarily on plant ecology, taxonomy, and microbiology. The papers contain valuable historical studies, especially floristic surveys that document Indiana’s vegetation in past decades. Authors were Butler faculty, current and former master’s degree students and undergraduates, and other Indiana botanists. The journal was started by Stanley Cain, noted conservation biologist, and edited through most of its years of production by Ray C. Friesner, Butler’s first botanist and founder of the department in 1919. The journal was distributed to learned societies and libraries through exchange.
During the years of the journal’s publication, the Butler University Botany Department had an active program of research and student training. 201 bachelor’s degrees and 75 master’s degrees in Botany were conferred during this period. Thirty-five of these graduates went on to earn doctorates at other institutions.
The Botany Department attracted many notable faculty members and students. Distinguished faculty, in addition to Cain and Friesner , included John E. Potzger, a forest ecologist and palynologist, Willard Nelson Clute, co-founder of the American Fern Society, Marion T. Hall, former director of the Morton Arboretum, C. Mervin Palmer, Rex Webster, and John Pelton. Some of the former undergraduate and master’s students who made active contributions to the fields of botany and ecology include Dwight. W. Billings, Fay Kenoyer Daily, William A. Daily, Rexford Daudenmire, Francis Hueber, Frank McCormick, Scott McCoy, Robert Petty, Potzger, Helene Starcs, and Theodore Sperry. Cain, Daubenmire, Potzger, and Billings served as Presidents of the Ecological Society of America.
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i the flowcring' plants of Indiana. 1937. IV. The poplar association and • Jour. £Col. 20: 380-415. 1932. THE STEM SMUTS OF STIPA AND ORYZOPSIS f fmlls alld Plew/ (;,'oqraph), 637 . '.. - pp. IN NORTH AMERICA'''' tltallls tr~lIslalcd papers 0 j Raullkiaer phy, and IS the source of ,all reI' erence By GEORGE W. FISCHER2 leaf size classes of certain plant Dureun of Plant Industry, Soils, 'D. Ecology 8 (I): 12-35. 1932, and Agricnltural Engineering
Over much' 0 f that great natural resource called the "Western Range," comprising some 728 million acres (1), species of Stipa and Oryzopsis are prominent and important members of the grass cover. These are commonly found affected with stem smut; often as much as 15-20 per cent of the plants are affected, and occasionally as much as 90 per cent. infection is encountered. In view of the value of these grasses as components of the western range, and the general interest manifest in the nature of the stem smuts so common on them, it seemed desirable to make a study of the identity of these smuts. It soon became apparent that more smut species are responsible for stem smut on Stipa and Oryzopsis than had hitherto been recognized as occurring in North America. Also'it became evident that for more than 80 years stem smnts of Stipa and Oryzopsis have been collected and curated in this country under the name Ustilago hypodytes (Schlecht.) Fr" while as a matter of fact six distinct species and one variety, in two genera were really represented. The various mor phologic aspects of the complex of stem smut fungi masking under the name U, hypodytes on a wide variety of grasses all over the world already have been presented (4). The present paper is a taxonomic treatise on the known fungi qiusing stem smut in Stipa and Oryzopsis in North America. The following key will serve to differentiate them.
I Cooperative investigations of the smuts of forage grasses, by the Division d Forage Crops and Diseases, Bureau of Plant Industry, Soils, and Agricultural Engineering, Agricultural Research Administration, United States Department of Agriculture, in cooperation with the 'Washington State Agricultural Experi ment Station, Pullman, Washington. Published with the approval of the di rector as Scientific Paper No. 624. ,,- A contribution in recognition of the 25th Anniversary of the Botany Dcpartment of Butler University, • Pathologist, Division of Forage Crops and Diseases, Bureau of Plant Industry., Soil.s, and Agricultural Engineering. 25 KEY TO THE STEM SMUT FUNGI ON STIPA AND ORYZOPSIS SPP. IN NORTH AMERICN r. Spores ih definite, persistent, large baits Uroc)'slis !1'Crsedi I. Spores free . •...... 2 2. Spores small (3.5-71'), smooth and unadorned...... 3 2. Spores larger (6-141'), exospore rough, cracked, verruculose, or lobed or echinulate at opposite poles . 3. Sori covered by persistent membrane of fungus tissue ...... U,-lilago Ini."i?lla 3. Sori naked after emerging from leaf sheath Usli!ayo IIJllllmll/aria' . "4. Spores large (10-141'). verruculose Us/ilago jacksonij 4. Spotes smaller (6·'10u). more or less bipolar ' 5 S. Spores .with a cracked exospore often resulting in an ear-like appe.ndage at opposite poles Usltlago williamsi; S. Spores with a erest of ee';'inulations or merely with apically thickened wall at opposite poles . 6 6: Spores yellowish to olivaceous-brown, finely papillose to minutely echinulate; bipolar areas minutely echinulate to echinuate Ustilafjo .fpcfJ(I.~::·i"i·i 0. Spores dark-browil. smooth or very finely papillose: bipolar areas consisting .of smooth apieal thickenings ...... U. spL·ga.~s/:7/.ii val'. a.iJre..li,;
I. . USTTLAGO MINIMA Arth. Bull. rowa Agr. CoIl. Dept. Bot. ll~R-l: liZ. 1884. Sori surrounding the internodes, aborting the inflorescence, covere(l b.v a per'sistent \vhitish membrane of fungous tissue; spores eseaping from ruptmecl or detached ends of membrane, spherical, light brown, smooth, 3.5-51'. Fig. 1, .\; fig. 3, A; fig. 6, A. .: On: 01'y:Jopsis hyml'1lOides (Roem. and Schult.) Ricker Ariz.) Colb:, New Mex.. 'Stipa comala Trin. and Rupr. Neb. '0tipa 11e011rexicana (Thurb.) Scribn. Ariz. Stipa spa.rtca Trin. Iowa, S. Dak. Stipa sp. Calif., Colo. This species has been much con (used in the various herbaria with the next -species, U. 1w11t1'lwlaria. (U. Itypodytcs Auct.). There ap pears to have been a tendency to consider the membrane as evanescent, and therefore of little taxonomic value. Hence many herbarium speci Figure 1. Phol " Examination under oil immersion lens is recommended in connection with Ustilago causing sten microsc.opit characters mentioned in this key. lago mininw; D. U. . • See also U. spega2sinii var. ogres/is. Some col1ections of this variety but few appendages; have inconspicuous bipolar areas and might be keyed out as U. 1I1t1ll1J11tlat·ia. open; F. U. jackson 26 NGI ON STIPA AND .. Q)'"'" ~ CJ RTH AMERICA3 €} Q&> ';~?['~ @~ G) ...... Urocystis fraserii COO ...•...... 2 Q 0,
e inflorescence, covered by a spores escaping from ruptured "D'~ 'rown, smooth, 3.5-5,u. Fig. 1, o tld Schult.) Ricker A'nz.,
riz. .,
the various herbaria with dytes Auct.). There ap ,:".~ /. ..,\.(u"'-'" membrane as evanescent, ~/"" P ce many herbarium speci ...., r
Figure 1. Photomicrographs of the chlamydospores of the speeie~ of rom mended in connection with Uslilago causing stem smut on Stipa and Oryzopsis in North America. A. Usti, lago min-ima; B. U. nummularia; C. U. williamsii, form with cracked exospore e collections 0 f this variety but few appendages; D. U. spegazzillii; E. U. willia1llsii, form with appendages !d out as U. I/umml//aria. open; F. U. ;acksollii. x approx. 600. . . ZJ finely papillose to minutely echinnlat, mens have been ent:ountered which had been entered as U, minima brown, mostly 4-6" in diameter, or 35.. and which clearly belong in U. l/.mmmtlaria. The membrane which On: Stipa 1ltucronafa HBK. surrounds the sorus in U. minima is not evanescent; on the contrary Stipa spartea Ill., Iowa, W1 it is a tough, persistent membrane of fungous tissue in the specimens I have examined. As pointed out by Clinton (3), Arthur did not mention this membrane, although it is present in his specimens. Germination of the spores has not been observed. Fresh material or recent collections were riot available.
2. USTILAGO NUMMULARIA Speg. An. Mus. Nac. de Buenos Aire~. (~er. 3) 1: 59. 1902. Ustilago hypodytes Auct. Sori surrOlmding the internodes and sometimes extending inlo the aborted in ilorescence, naked except for enl'eJopiIl!-{ lea f sheaths. dusty. da'rk brown to almost black; spores globose to sub-globose, yellowish to olivac~ol1s-brown, smooth, chiefly 4-5... in diameter, or 3-4 x 4-5.... Fig. I, B; fig. 3, B; fig. 6, B. On: OrY2opsis hym.enoides Colo. Idaho, Mont., Utah, 'Nash., v..f yo., Sask. Stipa comata Calif., Idaho, Mont., Or~., Wash., Wyo. Stipa lleomexicana N. Mex. Stipa sp. Calif. This stem smut is most common on Indian Rice Grass, Oryzopsis h)'me1loides, and needle grass, St-ipa cOlno.ta.. High percentages of in fection have been observed in Vvashington, Oregon, southern Idaho, and northern Utah, occasionally running as high as 90 per cent. Ustilago Htt1/tmnlaria has only recently been recognized as oc cnrring in North America. Fischer and Hirschhorn (4) showed that this species is one of several often erroneously referred to U. h),po dytes. Spore germination in Us/ita-go nummularia has been described by Fischer and Hirschhorn (1.c.), and is illustrated in fig. 2, C & D. Figure 2. photomicrographs oi .\, B, Us/ilo-go spega.~:;i"ii. from Slit 3. USTILAGO SPEGAZZINII Hirsch. Notas del Museo de La tPlata. callw/a; D, }bid., from Orysopsis liyJ' Botanica 4: 415-419. 1939. S/ipa spceiosa, F, irom Slip([ "enr·,II:O:: i Caeoma ,,~,podyles Schlecht. FI. Berol. 2; 129. 1824. (in part). C. jacksonii, irom S/·ipo }.clterlllolli. Ust·ilago hypodytes Auc!. Stipa Yobusla ~cribl1. (S. val Sori chiefly surrounding the internodes, but sometimes also' involving more Slipa vir-idula Trin. :.1. Da or less the inflorescence, although usually the latter is entirely aborted, olive 3a. USTILA(;O SPEG.\ZZI~·i brown to dark brown, entirely naked except for the enveloping leaf sheaths; and Hirsch.. Mycologia 3i: 1945. spores globose to sub-globose or slightly ovoid, provided with bipolar sub-hyaline Uslilogo It)'podyfes Auct. crests consisting of a prolongation of the epispore into a group of echinulations, 28 ed as U..11tinima finely papillose to minutely echinulate, clear yellowish-brown to olivaceous membrane which brown, mostly 4-6p. in eli'ameter, or 3.5-4 x 4·-7p,. Fig. I, D; fig. 4, A; fig. 6, C. ; on the contrary On: Stipa mucronata HBK. (S. setigera) Mexico in the specimens Stipa spartea Ill., Iowa, Wise. Arthur did not i specimens. . Fresh material e. de Duenas Aires.
19 into the aborted ;ty. cia'rk brown to alivaceolls-browll, :ig. 3, B; fig. 6, B. :., Utah, \Vash.,
Wyo.
trass, Oryzopsis rcentages of in ;onthern Idaho, ~ per cent. ognized as oc 4) showed that ~CJ to U. hypo- n described by ~. 2, C & D. Figure 2. Photomicrographs of germinating' spores of stem smut fungi: :eo de La .;Plata, A, B, Ustilago spegaz:Jil1ii. from Stif'a:vir'idula; C, U. numtnl~laria,from Stira comata; D, ibid., from Orszopsis hStlte1w·ides; E-I, U. wilwmsii: E and I, from & part) . Stipa speciosa, F, from Stipa cemlla; G H, from Ory:;opsis hY1JlClloides; ]-M, U. jacluol1ii, from Stira lette,·mani. X approx. 500. Stipa 1'obusta Scribn. (S. vaseyii) N. Mex. involving more Stipa viridula Trin. N. Dak., S. Dak., Mont. . aborted, olive g leaf sheaths: 3a. USTILAGO SPEGAZZINII var. AGRESTIS (Syd.) G. W. Fisch. ;lIar silb-hyaline and Hirsch.. Mycologia 37: 1945. ,f echinulations, Ustilago ltypodytes Auet. 29 Dif fering from the species as follows: Spores dark brown, usually smooth but under oil immersion sometimes appearing very fineJy papillose; erests rather inconspicuous, sometimes appearing as lacerated apical thickenings, sub-hyaline to concolorous with the spore. On: Stipa californica Merr. and Davy Calii. Stipa occ'identalis Thurb. Calii. Stipa f1Iucronata (S. setigera) Mexico Stipa spartea, III. Stipa pulchm Hitchc. Calif. Stipa 'ui:idula N. Dak. Fischer and Hirschhorn (4) have recently demonstrated the con fused re,lationship oi Ustilago spegazzinii and the var. agrestis to U. hypodytes, U. st-ipac, U. bromi-crccti, and U. agrestis. Spore germination has been described by Fischer and Hirschhorn (I.e.). After 24 hrs. or more a single germ tube emerges, elongates, and usually soon becarnes differentiated more or less into a 3-4 celled promycelium. These cells, however, have not been observed to pro duce primary sporidia, but, instead, long slender branches. These elongate and re-branch to initiate a mycelium, which soon begins to bear chains of aerial sproidia. Fig. 2, A & B.
4, USTILAGO WJLLJAMSn (Griff.) Lavrov Trav, Inst. Sci, BioI. UniY, Tomsk 2: 22. 1936. Uslilago Itypodyles Auet. Soros/,ori1f.11t william,si'i Griff. Bull. Torr, Bot, CllIb 29: 290-301. 1902, Uslilago ap/,clIdiwlala Speg, Myc. A,'g. en A,llI. Mus. ~al. de Buenos Aires, Ser. 3, 12: 288. 1909. Tmn:;c/ziclla olho/,hora Lavrov, Trav. Tnst. Sci, Bioi, Univ, TOlusk 2: 29. 1936,
Sori surrounding thc upper intcrnodes, oflen involving also remnants of the aborted inflorescence, dark-b,'owl' Lo black. naked except for enveloping lea f sheaths; spores globose to sub-globose, provided with all epispore that is smooth. but deeply cracked into large pieces. oiten appearil1g- as bipolar ears ur appendages, dark olivaceous-browll, 7-10" in ·diameter, Fig, 1, C & E; fig, 4, B: fig, 6, D, On: Or,\'::opsis blo01/'leri (Boland.) Ricker, \Vash. Oryzopsis hYl1tenoidcs Mont., Wyo. Stipa califm'nica Cali f. A Figure 3, A, Ustila.go membrane around sori; B. U. 1I1ltll nat. size,
J(}.. Spores dark brown, usually smooth very fiudy papillose; crests rather lted apical thickenings, sub-hyaline
)avy Calif. eXlco
ecently demonstrated the con Iii and the val'. agrestl:s to U. ~nd U. agrestis. t ~ ... d by Fischer and Hirschhorn ;erm tube emerges, elongates, 1110re or less into a 3-4 celled ve not been observed to pro :lg slender branches. These :eliul11, which soon begins to I' A & B.
I Lavrov Trav. Inst. Sci. BioI. \
Bot. Club 29: 290-301. 1902. en :\1111. \'lus. Nat. de Buenos
1St. Sci. BioI. Un;v. TOlllsk 2:
'ten invol"illg also remnants of K. naked except for enveloping o\·ided with an epispOt'e that is ten appearing as bipolar cars or ametcr. Fig. 1, C & E; fig. 4,
Ricker. Wash. A B ,....
Figure 3. A, Ustilago l1Hl1111la, on Stipa Iteomcxicatla. Not~ .persistent membrane around sori; B. U. nl!1mm~lal'ia" on Or)'zopsi:, hymell'.oides; .App:r()x; nat. size. .
31 Stipa comata Ore., Mont. On: Stipa letterman;' Utah. Stipa cernua Stebbins and Love Calif. This is the rarest of the stem Stipa corO/wta Thnrb. Calif. in :\orth America. According t· Stipa lettermani \"fyo. descrihed the species, it was fir~t Stipa occidentalis CaliL, Ore. Only one viable collection" of Stipa richardso1'1.i Link IVJ ant., "Vyo. the following obsen-ations of ! Stipa speciosa Trin. and Rupr. Calif. ltased on this one collection. At Stipa viridula. Mont. dextrose-malt extract peptone a, Stipa tkurberiana Piper Wasil. i or three days, after which app (lbsen'ed in variotls stages of gen Many collections of stem smut on O"')ltiOpsis and Stipa spp. are g-illS to protrude, and from this tit deposited in the herbaria as (( Ustilago h3'podytes," but belong to U. which soon begins to hranch and r 'Willia111.sii. The larger spores, the cracked exospore, and especially germinating spores the germ tuh the characteristic appendages make this stem smut species distinct the extent of bearing" sporidia ((i from U. spegazzinil: var. agrest/:s. Some collections have more dis compared with the rapidity of ~I tinctly appendaged spores than others. In fact occasional collections llH.;nt of Ustilago williol1lsii. Ap are encountered in which only the cracked exospore and an occasional to reach the extent of develop appendaged spore identify the species (fig. 1, C). the time required for gemlination Germination of the spores takes place rapidly, beginning in 4-6 lIlination and the development of hours. On dextrose-malt extract-peptone agar a slender germ tube due to invasions by contaminatin emerges f rom one or the other of the appendaged areas and soon ,;lowly developing germ tubes an develops usually three cross-walls. From each of the resulting four cells a sporidium or a branch arises, more often the latter (fig. 2, E-G, 6. UROCYSTIS 1'IV,SERII CI 1\118. 1939. 1). That these cells of the pro-mycelium represent di fferent sexes S oros(>oriHlIl yroJllrlr.nrm Ell. & seems probable from the fact that fusions between these cells are Sori more or kss surrounding th frequently observed, usually by means of a fusion tube, such as is ,,[ a stem SJIlut, but actually composef\ th~ seen connecting two proximal cells in fig. 2, H. The branches .of s',,'; running up i11lo and jJ1\'olving t the promyceliul11 rapidly develop more branches, and a vigorous membrane composed o[ the host epid! mycelium is thus.started. Very early in the development of this "<'1oping Ita ( sheath as a more or It mycelium short, erect hyphae make their appearance and on these opaque, brown to dark brown, 35-70, smooth, with walls quilc thick in nJiI" are borne short chains of aerial sporidia in great abundance. These chic Oy 5-10,.. ill diameter or 4-6 x 5~ aerial sporidia appear to be identical with su.ch primary sporidia as thin-walled, light brown. 8-20 or nJo may be borne on the promycelium. 5. A: fig. 6, 1'.
5. USTILAGO ]ACKSONII Zundel and Dunlap. :'-Jorlh i\merican Flora 011: Slipa clandcstina Hac' 7(14) : 982. 1939. St-ipa contata Colo., \IQut., Stipa sjJ(lrtea :\ebr. Sari sur rounding the upper internodes and more or less consuming the aborted inflorescence, covered only by the enveloping lea f sheaths: spores Stipa viridula Colo. olivaceous-brown to dark-brown, often quile irregular in shape, globose to ovate, verruculose, mostly 10-12,.. in diameter, but often 14,.. in length. Fig. 1, ; On S/i(>o leI/en/Will.. :\iollle F; fig. 5, B; fig. 6, E. \,V. R. Rader, fid. G. \Y. Fischer, ;\(1 32 On:· Sfipa letlcrmani Utah, Colo. This is the rarest of the stem smuts attacking Stipa and Or}l:;opsis 111 ~()rth America. According to Zundel (6), who only recently described the species, it was first collected in 1921. in Colorado. Only one viable collection" of Ustilago jacksonii was available and the following observations of spore germination in this species is based on this one collection. At room temperature, spores sown on dextro~e-l11alt extract peptone agar showed no signs of germination for three days, after which approximately 5% of the spores were psis and Stipa spp. are observed in various stages of germination. One end of the spore be ~~tcs,J) hut belong to U. gins La protrude, and from this there emerges a short thick germ tube kospore, and especi'ally which soon begins to branch and re-branch (fig. 2, J & K). On some smut species distinct germinating spores the germ tube resembles a promyceliU1l1, even to ections have !nore dis the extent of bearing sporidia (fig. 2, L). The process is a slow one tt occasional collections compared with the rapidity of germination and subsequent develop !spore and an I. :'-! ortb ..\ 11Icrican Flora all: Slipa clandcstina Hackel Coahuila, )\'Iexico Stipa COl/wta Colo., lVf Qnt., Sask., 'vVyo. : or kss C0I1SI111lill~ the Stipa spartea Nebr. 19 lea f sheaths: spores Stipa viridula Colo. !If ill shape, globose to n 14", ill length. Fig. I, • On Sti/'(l leiterul(llli. lI.fonte Cristo Mt.. Hich Co., Utah. 8-17-41 leg, \.\-". R Rader, fid. G. W. fo'ischer, No. 209, Bur. Plant Ind. Myc. Call. :-10. 85065. 33 The presence of two distinctly balls excludes this smut from the originally placed. Repeated atte spores have been unsuccessful among thousands of spore balls, plate. This one germinating ~P0f! t here considered as the spores an Ustilago type. However, no at \I found on the same agar plate, an, have failed to substantiatc the ob. prove that spores of this smut ful species in the Ust-ilaginaceae then species of a new genus, onc w~ Uroc3,stis in the Tillitiarcae. In that of existing genera the fung Transferring this smut to the g, binomial U. gyanulosa but this to a distinctly di fferent and rare s described by Clinton (2). Zundel (6) has recently des' (omata, from Saskatchewan. _;~ of this species I am cOlw:nced th1 ~ under discussion and as long as ~ cystis, then by priority Zundel's 15 el1tly Zundel did not recognize tl sporiUNt grauulosum, for each isl publication' (6). COMPARATIVE I)ATHOL ST£1\11 S:M UTS OF S The apparent superficial natl the subj ect of interesting conjec of the host plants. A casual ex OY3Jzopsis affected with these smt tissues of the host were entirely .~ One wonders, therefore, ,tbout th~ 8 in these smut diseases. .\ thoTOul tribute some valuable data of a Figure 4. A, Ustilago sPcgaz::rillii, on Stipa viridula; E, U. williams;i, on work the parasitism of the fungi. Sripa speciiJsa. Approx. nat. size. hosts have been included in on] 34 The presence of two distinctly different kinds of cells in the spore balls excludes this smut from the genus SorospOl'ium, where it was orig-inally placed. Repeated attempts to observe germination of the ( spore-s have been unsuccessful except for one germinating- spore among thousands of spore balls, spores and sterile cells on an agar plate. This one germinating ~pore appeared similar to the large cells here considered as the spores and germination was, definitely of the Usl-ilago type. However, no other such germinating spores were found on the same agar plate, and previous and subsequent attempts have failed to substantiate the observation. If future studies should prove that spores of this smut f11l1guS germinate such as to place the / species in the Ustilagi'llareae then it probably would become the type species of a new genus, one which would be the- counterpart of Urocystis in the Tilritiaaae. In the meantime, it must be admitted that of existing genera the funglls most closely resembles U,'ocyst·is. Transferring this smut to the genus U1'oC':l~lis should result in the' binomial U. granulosa but this name is already occupied, belonging to a distinctly di fferent and rare smut in the spikelets of St-ipa. CO'mata, described by Clinton (2). Zundel (6) has recently described Urocystis fraser ii, on Stipa romata, from Saskatchewan. After a careful study of type material of this species I am cOJ1Y:nced that it is identical with the stem smut under discussion and as long as this smut is considered to be a U,'o cystis, then by priority ZUl1del"s binomial should apply to it. Appar ently Zundel did not recognize the identity of U. frascrii with Soro sporiU'Nt gral/.lrtoSLl'l1I, for each is treated independently in the same publication' (6). COll'IPARATIVE PATHOLOGICAL HISTOLOGY OF THE STEM SMUTS OF STJPA AND ORYZOPSIS The apparent superficial nature of the stem smuts has long heen the subject of interesting conjecture as to the pathological histology of the host plants. A casual examination of the stems of St-ipa and OrJ'zopsis affected with these smnts would suggest that the underlying tissues of the host were entirely normal, even including the epidermis. One wonders, therefore, about the nature and extent of the parasitism in these smut diseases. A thorough study of this problem should con tribute some valuable data of a fnndamental nature. In the present . B, L:. 'Willi(J.lIISii, on work the parasitism of the fungi and the pathological histology of the hosts have been included in only a very preliminary fashion. Por- JS tions of culms of Stip€!, and Or)'::o by the six species treated above infiltration and embedding proces gOJ tome. The sections were staine "0 OJ .... The comparative microscopic ~, ... .:!: Stipa and Ory:::opsis is shown in I .~ serii and Ustilago minima, the sm iii ~:- In the case of Ustilar;o nU11lmula _....-....-_. ------ U. jacksonii the stem tissues se ~ O. parasitized by ~ hY11ll'noidcs U. -~ .. tha~ ~ epidermis. Finally, it is seen is such that the fungus develop .~ .. ~ destroying the chlorophyll paren' § mechanical tissue. Hirschhorn (5) describes th ...,c chlamydospore mass and the ho~ -'<.., .....'" these stem smuts on Stipa in Argj C> is quite variable according to h ~'"' of some significance that in the 1:; ;::::, stroma was found in any of the , _/ m reports of a stroma by other in g<:; younger sori, in which the su ,-- "\J" c converted into a spore mass. Zf .., formation in at least 'some of th e .:;. thus the underlying mycelium c< ~ ~ c: bearing stromatic layer. It ca o specialized tissue, however, if ~, ...,t part of the spore mass. Obvio , J e needed on the ontogeny.of the st " / ..t., /' .1:..., issues. ..,?> ... ::::" -:r;' ... U) ....Cl) /~ .~ ~ < , ...... " 3(; tions of culms of Stipa and O,'yzopsis affected with stem smuts caused by thc six species treated aboyc were carried through the para ffin in filtration and embedding process, and sectioned with a rotary micro '""'-' S! tome. The sections were stained with Thionin and Orange G. ....'.J ,..::, The comparative microscopic appearance of six stem smuts ot Stipa and 01'}'zopsis is shown in Fig.. 6. In all except Urocystis fra ~t sCtii anel Ustilago '1'11:inima. the smut appears to be entirely superficial. if.' In the case of Ustilago 111lmmularia, U spegazzinii, U. W'illimnsl:i .. and ....; U. jacksonii the stem tissues seem to be quite intact. The sections qf ~ O. hymcnoidcs parasitized by U, 'minima. indicate destruction of the ~ epidermis. Finally, it is seen that the parasitism of Urocystis fmscrii & is such that the fungus. develops beneath the epidermis, apparently • :..--; destroying the chlorophyll parenchyma cells, and even some of the o mechanical tissue. ' Hirschhorn (5) describes the presence of a stroma between the ..,<:; chlamydospore mass and the host epidermis in the case of some of -'< 011 ~'" these stem smuts Stipa in Argentina, and states that this character c is quite variable according to host species and locality. It may be ~ ~ of some sig-ni ficance that in the present studies 110 trace of such a ~ ...) stroma was found in any of the six smut species. It is possible that q reports of a stroma by other investigators were based on studies of ~ younger sori, in which the superficial mycelium had not entirely ~ ~ converted into a spore mass. It has long been known that spore § formation in at least some of the stem smut fungi is centrifugal, and <:; .:,.... c;; thus the underlying mycelium could easily be inteq)reted as a spore bearing stromatic layer. Jt can scarcely be considered as such a ' specialized tissue, however. if the layer itself ultimately becomes ~ part of the spore mass. Obviously some careful investig'ations are ;; ...;::, needed on the ontogeny .of the stem smuts, to clari fy such fundamental .:? Issues. ....'-, ~ s.~ ....-; .,.; ::<.> c( E 37 1. CLAPP, EARLE in, The West< Congress, 2nd 2. CLll\TON, G. P 3. Nat. His!. 31 4. FISCHER, GEaR species of Usl 1945. (In pre 5. HIRSCHHORN, Darwiniana 3: 6. ZUNDEL, GEaR' Flora 7 (14) : ' and enlarged pal Or~lzopS'is h}'men( around same; B, viridula; D, U.11 Figure 6. Comparative pathological histology of stems of Stipa and 01"}'ZOP ter'mall'i; F, Uroe sis affected with stem smuts. Cross sections of the sori and &tems (upper row)', enlarged por1ions 38 LITERATURE CITED 1. CLAPP, EARLE H. The major range problems and their solution. A resume in, The Western Range. United States Senate Document 1\0. 199 (i4th Congress, 2nd Session) xvi + 620 pp. 1936. 2. CLINTON, G. P. North American Ustilagineae. Jour. Myc. 8: 128-156. 1902. 3. North r\merican Ustilagineae. Proc. Boston Soc. Nat. Hist. 31: 329-529. 1904. 4. FISCHER, GEORGE W., ANll HIRSCHHORN, ELlSA. A critical study of S'UllL' species of USfilago causing' stem smut on various grasses. Mycologia 37: 1945. (Jn press.) 5. HIR~CHHORN, ELlS". Las especies del genero "Ustilago," en la .-\rgcntina. Darwiniana 3: 347-418. 1939. 6. ZUNDEL, GEORCE L. UstiJaginales. Additions and corrections. N..-\Jl1~r. Flora 7(14) : 971-1045. 1939. and enlarged portions (lower rows), as follows: A, Usltlago 'I1I1I/./ma on Orysopsis !lyme/fairies, note thieknt55 of spore mass ami the fungous membrane around same; B, U. nmnmn/an:a on Slipa comata; C, U. spega.~:dll,ii on St·;pa 7}il'idula; D, L'. will·io·l1Isii, 011 Sfipa riclwrdsoni; E, U. jackson·ii, on Slipa lel i and Or:'i:::op Icrmont; F, U"ocyslis frase·ri·i, on SI;p(l comola. Stem sections x approx. 50; (upper row), enlarged poriions x approx. 200. 39