Frey—Physiology of Venturia Inequalis, 
317 
bud, and the buds form the asci. The nuclei of the ascogenic cells 
divide simultaneously and one of the daughters of each mother 
nucleus passes into the ascus, the pair left in the ascogenic cell 
may divide again. The two nuclei that enter the ascus fuse to form 
the primary ascus nucleus. 
Miyake (1901) states that the multinucleate oogonium of 
Pythium de laryanum is differentiated into ooplasm and periplasm. 
A nucleus from the periphery migrates into the ooplasm to func¬ 
tion as a female nucleus, which previous to fertilization divides. 
Only one antheridial nucleus functions. 
It is interesting at this point to take up the yeasts, a group of 
Ascomycetes which have asci but no definite sex organs. Some 
yeasts, according to Guilliermond (1912), form the ascus by the 
fusion of two vegetative cells. A bud or beak is formed which 
fuses with the bud of another cell and the nuclei migrate into the 
tube and fuse. There is considerable variation in the manner of 
fusion and in the number of spores formed in the ascus. Wager 
and Peniston (1910) state that during spore formation in the 
Saccharomycetes the nuclear vacuole and network disappear. The 
nucleolus becomes closely surrounded by chromatin granules and 
then divides into two nearly equal, or equal, daughter nuclei each 
of which consists of a portion of the nucleolus with the surrounding 
chromatin. Each of the nuclei divides again to form the four 
spore nuclei of the ascus. 
Guilliermond (1911, 1917, 1918) states that pairings of cells 
may occur in some forms of yeasts by the cells forming a beak and 
that nuclear fusion occurs, followed by migration of the fusion 
nucleus into one of the cells, leaving the other empty. The egg 
then forms an ascus. From the similarity of the developments of 
yeasts to Endomyces and Eremascus he thinks these forms are affili¬ 
ated. 
From the evidence available no definite phylogeny can be traced 
for the yeasts. It appears that only one nuclear fusion takes place 
and that the oogonium itself becomes the ascus. In such simple 
related forms as Gymnoascus reesii and Gymnoascus candidus Dale 
(1903) finds that sexual fusion occurs. The ascogenous hyphae 
arise from cells which have paired and fused. 
Observations on Saccharomyces cerevisiae and related forms 
made by the writer indicate that dumb-bell forms are quite com¬ 
mon in old cultures, especially if the culture solutions are of high 
acidity and unbalanced physiologically. Whether these forms have 
