SPORODINIA. CLOSTERIUM AND COSMAR1UM. 71 



SPORODINIA. 



Morphologically considered, the sexual process in Sporodinia 

 grandis and in other typical Zygomycetes seems to be similar to that 

 in the Conjugates, but in Sporodinia the gametes are multinucleate, 

 and the behavior of the nuclei in the young zygote varies considerably, 

 according to the accounts given by the different observers. After the 

 cytoplasmic fusion of the gametes, the nuclei of each arrange them- 

 selves into a spherical layer surrounding a globule of oil, and then 

 fuse, producing a hollow sphere full of oil, which Le"ger ('95) has 

 called an embryonic sphere (sphere embryonnaire). These embryonic 

 spheres lie near the poles of the zygote. During the germination of 

 the zygospore the two embryonic spheres fuse. The fused mass 

 reveals numerous nuclei, which pass into the sporangiferous mycelium 

 and begin to divide. In the azygospore only one embryonic sphere is 

 developed. Wager ('99) regards the union of the nuclei to form the 

 embryonic sphere as the sexual act, and the azygospores are, there- 

 fore, truly sexual, the process of conjugation being of secondary 

 importance. Dangeard ('94, '95) does not accept Lager's interpreta- 

 tion of the embryonic spheres, holding that the fate of the nuclei has 

 not been determined. 



According to Gruber ('01) no embryonic spheres are to be seen in 

 the newly formed zygote. The numerous nuclei, on the contrary, are 

 uniformly distributed throughout the cytoplasm. After five or six 

 weeks the same condition of things was still found to exist, and what 

 took place finally among the nuclei Gruber was unable to determine. 

 Neither fusion, disorganization nor division of the nuclei was observed 

 even six months after the fusion of the gametes. 



From what is now known concerning the sexual union of multinu- 

 cleate gametes in other groups of plants, in which the sexual process 

 has been unmistakably followed in every detail, it is very probable that 

 a multiple fusion of the nuclei in pairs obtains also in Sporodinia? 



CLOSTERIUM AND COSMARIUM. 



In the desmids the process of fecundation agrees essentially with 

 that described by myself for Spirogyra, except as regards the time of 

 the fusion of the sexual nuclei and the behavior of the chromatophores 

 in the zygospore. During the development of a firm cell-wall about 

 the zygote, according to Klebahn ('91), the chromatophores undergo 

 a marked change, the result of which is the formation of two large 

 rounded balls, which are at first rich in starch and of a yellowish 

 color. The part taken by the four original chromatophores in the. 



1 See Chapter III, Albugo Bliti, and Chapter IV, Pyronema. 



