Cytological Studies of the Zygospores of Sporodinia 
grandis 
BY 
MARY LUCILLE KEENE. 
With Plates XXXV and XXXVI. 
T HE study of the nuclear processes which take place when multinucleate 
gametes fuse, constitutes a problem of very great interest. In general, 
in sexual reproduction of both plants and animals, the sex cells which fuse 
are uninucleate, but there are numerous exceptions to this to be found in 
the Plant Kingdom, especially among the Fungi. In the Ascomycetes as 
Pyronema , in the Oomycetes as Albugo , in the Zygomycetes as Sporodinia , 
we find that the sexual fusion regularly takes place between gametes, each 
of which contains several nuclei. While most of these forms have been 
investigated more or less thoroughly, there is no final agreement with 
reference to the essential features of the nuclear phenomena. 
Harper (21) has carefully investigated Pyronema , and has described 
the fusion of multinucleate gametes, the nuclei of which fuse in pairs. 
Claussen (3), in recent studies on the same form, also described a fusion of 
multinucleate gametes, but was not able to determine the fusion of the 
nuclei in pairs. He considers the nuclear fusions which occur later in the 
young ascus as the sexual act. 
In the Oomycetes, there has been considerable evidence brought 
forward as to the nature of the fusions of the sex cells. Stevens (28) 
describes a fusion of multinucleate gametes in Albugo Bliti, and, later (30), 
in Albugo Ipomoeae-panduranae. He also describes the development of the 
oosphere of Albugo Tragopogonis , in which the supernumerary nuclei are 
said to disorganize, a uninucleate condition resulting. A single male nucleus 
then fuses with the egg nucleus. The fusion nucleus undergoes many 
divisions, so that the winter oospore is multinucleate. 
Davis in 1900 (14), and Stevens in 1901 (29), both find that the mature 
oosphere of Albugo Candida is uninucleate. One male nucleus is said to fuse 
with the nucleus of the oosphere, and a uninucleate oospore is produced. 
[Annals of Botany, Vol. XXVIII. No. CXI. July, 1914.] 
