Frey—Physiology of Venturia Inequalis. 
313 
It is necessary at this point to take up the work of other investi¬ 
gators that we may determine to what extent the theories proposed 
by the leading workers or pioneers have been substantiated. Nichols 
(1896) holds with Harper that sexual fusion occurs in the Ascomy- 
cetes, but it may not occur in all of them. In Ceratostoma no sex¬ 
ual fusion occurs and in Teichospora aspersa and Teichosporella sp. 
the ascocarp is formed by the division of a single hyphal cell of the 
mycelium. The ascus arises from a single central cell. 
Wager (1899-1900) described the formation of a single sexual 
nucleus in the ooplasm of the oogonium of Peronospora parasitica. 
The remaining nuclei of the female organ pass into the periplasm 
and degenerate. Both male and female nuclei undergo mitosos 
before fusion and a central body is present. The zygote is uninuc¬ 
leate. Stevens (1899) holds that the oogonia and antheridia of 
Albugo bliti are multinucleate when formed but later the oogonium 
is differentiated into oosphere and periplasm. All the nuclei pass 
into the periplasm and undergo mitosis. The nuclei that lie at the 
boundary between ooplasm and periplasm give one daughter 
nucleus to the ooplasm, the other to the periplasm. Fertilization 
occurs in this species; the male nuclei enter the ooplasm by means 
of the antheridial tube and fuse in pairs with the female nuclei. 
Several sex organs are produced on Cladonia crispum. Baur 
(1898) thinks fertilization is necessary to produce asci. Baur 
(1901) states that he observed fertilization of the carpogonium by 
spermatia in Parmelia acetabulum. Parmelia and Cladonia accord¬ 
ing to Baur (1904) have ascogenous hyphae arising from the carpo¬ 
gonium. He observed fusion of spermatia with trichogynes in 
Anaptychia and Endocarpion but could discover no fusion in 
Solarina and declared it to be apogamous. 
Juel (1902) holds that Dipodascus, which has multinucleate sex 
organs arising side by side from a single hypha, has functional 
oogonia and antheridia. One large male nucleus passes into the 
oogonium by a pore and fuses with a large nucleus in the oogonium. 
The oogonium produces a single ascogenous hypha, the latter pro¬ 
ducing a single ascus. The nuclei arising from the fusion nucleus 
decrease in size with each division and finally pass into the ascus. 
Juel thinks that Dipodascus is comparable to Albugo in the forma¬ 
tion of the egg. Sexual fusion occurs in Gymnoascus reesii and 
Gymnoascus candidus according to Dale (1903). The ascogenous 
hyphae arise from cells which have paired and fused. 
