Baird—History of Phycornyces Nitens (Agardh) Kunze. 375 
tioned by Miss Keene (1915) are the same as the reserve food 
bodies of zygospores described by me. 
As to the question of nuclear fusions in the zygospores of the 
various forms of the Mucoraceae, a review of the various reports 
shows that even in the same species there is little agreement as to 
when fusion takes place or how many nuclei take part. Several, 
as my review of the literature shows, do not find nuclear fusion at 
all in the early formation of the zygospore. Burgefi (1915) de¬ 
scribes nuclear fusions as taking place at or shortly after zygo¬ 
spore germination. Many of the workers have described nuclear 
fusions as taking place soon after fusion of the gametes. For this 
period I have described rapid nuclear division. 
Burgeff postulated a theory as a result of his work to account for 
the effects brought about by some nuclei fusing and others not 
fusing. If the nuclei do not fuse anywhere in the life history of 
the plants, as my results seem to indicate, the behavior of the 
nuclei in the germ sporange remains to be demonstrated before any 
theory to explain the significance of sexual process in the 
Mucoraceae can be advanced. 
Summary 
1. The nucleus in Phycomyces nitens and in Bhizopus nigricans 
is a dense, homogeneous, chromatin body. 
2. The nucleus divides by a method of fragmentation into sev¬ 
eral portions; the complete separation of these fragments is brought 
about by growth of a vacuole formed within the body of the mother 
nucleus. In some instances the separation of the daughter nuclei 
is aided by the streaming of the protoplasm. 
4. Vacuoles frequently form eccentrically in a nucleus in such 
a way as not to bring about nuclear division. 
5. Nuclear division continues during the growth of the fungus 
in the sexual generation. In the vegetative hyphae nuclear divi¬ 
sion is arrested by the discontinuance of water absorption by the 
mycelium; in the spores of the sporange, by a reverse of water 
absorption to water excretion; and in the zygospores by maturation, 
which is undoubtedly accompanied by cessation of water absorp¬ 
tion. 
5. In zygospore formation no nuclear fusions seem to occur. 
6. When nuclear divisions stops in the zygospore and in the 
vegetative hyphae, reserve material is stored in the vacuoles asso¬ 
ciated with the nuclei. 
