BRAZILIAN CHYTRIDS. VII. OBSERVATIONS RELATIVE TO SEXUALITY IN TWO NEW SPECIES OF SIPHONARIA

SEXUAL REPRODUCTION in the monocentric eucarpic rhizidiaceous chytrids appears to be comparatively rare, or at least it has been observed in only a few of the known species. In the majority of these chytrids the resting spores have been reported to develop asexually without prior fusion of gametes. However, more than forty years ago in Denmark, Petersen (1903) found a monocentric chytrid, Siphonaria variabilis, in insect exuviae the resting spores of which appeared to have been formed by fusion of the contents of two small thalli through anastomosed rhizoids. He reported and figured the presence of a small empty thallus attached by a tube or rhizoid to the mature spore and stated that sexuality was probably involved in the development of the resting spores of this species. He reaffirmed this statement later in 1909 and 1910. The observations of Petersen on S. variabilis were substantiated by Sparrow in 1935, who further reported that the same type of sexual reproduction occurs in Rhizoclosmatium also. He confirmed these reports in 1937 and expressed the belief that a similar fusion of thalli would likewise be found in Asterophlyctis. The discovery by the author in Brazil and in the United States of two additional species of Siphonaria in which the resting spores appear to be formed sexually confirms in general the observations of Petersen and suggests that the type of sexual reproduction exhibited by these species may possibly be widespread in certain genera of chytrids. Petersen distinguished Rhizoclosmatium, A sterophlyctis, and Siphonaria on the basis of differences in the structure of the rhizoidal system and sporangia. The sporangia of the first genus were described as globose, smooth, apophysate, and subtended by relatively fine rhizoids. Asterophlyctis was reported to be similar to Rhizoclosmatium except for its somewhat stellate and spiny sporangia and resting spores. Siphonaria, on the other hand, was described as nonapophysate with thick-walled, tube-like rhizoids, and because of the latter characteristic Petersen named the genus Siphonaria. These generic distinctions, based on vegetative structural differences, were subsequently recognized and accepted by most chytridologists. The report by Sparrow (1937, p. 34), however, that Siphonaria may sometimes be apophysate and the discovery by the author of a nonapophysate Asterophlyctis-like species with occasional tube-like rhizoids show that the presence of an apophysis and the nature of the rhizoids in these species are variable characters and of doubtful importance in distinguishing genera. The report that all the genera are characterized by the same type of 'Received for publication June 29, 1945. This work has been greatly facilitated by a Grant-inAid of Research from the Graduate Faculties of Columbia University. sexual reproduction is of greater significance in phylogeny and classification and should take precedence over variable vegetative character in diagnosis. In the event Sparrow's observations on Rhizoclosmatium and Asterophlyctis are confirmed, these genera should be merged with Siphonaria on the grounds of similarity of type of sexual reproduction. Asterophlyctis sarcoptoides, however, has been isolated frequently by the author and grown in pure culture on chitin and chitin agar, and so far no evidence of fusion of thalli has been observed. It is therefore questionable whether or not Asterophlyctis can be merged with Siphonaria on this basis. The species found by the author in Brazil are named S. petersenii and S. sparrowii, respectively, in honor of Drs. H. E. Petersen of Denmark and F. K. Sparrow, Jr., of the University of Michigan, who introduced and extended the study of chytrids which inhabit the exuviae of insects. Relatively few specimens of the Brazilian species were found in an unidentified insect case at Flores Nabuco near Manaus, Amazonas, but after the author had returned to the U.S.A., he found an abundance of both species in the exuviae of mayflies near Pawling, New York. As was noted earlier, the first of these species is A sterophlyctis-like, with spiny but nonapophysate sporangia, while the second one is similar to the type species, S. variabilis. The present observations relate entirely to living material, but a further study of plasmogamy, karyogamy, and meiosis from fixed and stained material is now in progress and will be described in a later paper. SIPHONARIA petersenii sp. nov.-Fungus saphophyticus; sporangiis extramatricalibus, spinosis, colore areo-luteo, longitudine pyroformibus, 5-20 X 10-36 ,u; zoosporis sphericis, 3-3.5 ,u; sporis perdurantibus sphericis, 10-15 Is, ovatis vel angularibus, 6-8 X 10-14 ,u. Thalli numerous, occurring inside of empty insect exuviae. Sporangia extramatrical to substratum, non-apophysate, orange-golden in color, predominantly elongately pyriform, 5-20 X 10-36 u, occasionally elongated transversely to rhizoid axis, with a long sharp apical and 3-12 lateral, simple or bifurcate spines, 4-15 u in length; exit papilla subapical, low and inconspicuous. Zoospores spherical, 3-3.5 /s, with a small (1.5 ,u) golden-red globule; swarming in a vesicle for several minutes before breaking out and swimming away. Rhizoidal system intramatrical, monoaxial, arising from base of sporangium, richly branched and extending for a distance of 80 ju. Resting spores spherical, 10-15 /A, oval, or slightly angular and spiny, 6-8 X 10-14 /A, with a reddish-brown (2 ,u), slightly uneven, crusty and almost verrucose wall; containing numerous granules and globules; formed sexually by the fusion of the contents of one or more "male" (?) thalli