Frey—Physiology of Venturia Inequalis. 
311 
by Clausen (1912) appeared in which he sets forth some new views. 
Clausen adopts an entirely new viewpoint. His theories combine 
the ideas of de Bary, Harper and Dangeard, and, if substantiated, 
will form a distinct advance in our knowledge of the sexuality of 
the fungi. Clausen retains the idea that the ascogonium and 
antheridium are sexual organs and that only one nuclear fusion 
occurs. This takes place in the ascus and may be considered com¬ 
parable to the fusion occuring in the basidia and in teleutospores. 
The sexual act initiated in the sex organs is completed in the ascus. 
It may be well to review in more detail the ideas of Clausen in 
order that a complete understanding of the various theories may 
be gained. The views of Blackman and Welsford (1912) are op¬ 
posed to those of Clausen and will be reviewed later. Clausen 
(1905) described the formation of the sex organs in Boudiera. 
Short branches arise from the vegetative hyphae which branch 
dichotomously. The branches then twist about each other forming 
spiral coils, two branches in a coil, one forming the ascogonium and 
trichogyne, the other the antheridium. The ascogonium contains 
two or more nuclei. Ascogenous hyphae arise from the ascogonium 
after fusion with the antheridium has taken place. Nuclear be¬ 
havior and the formation of the asci is similar to that of Pyronema 
confluens. Clausen (1906) states his belief in the sexuality of the 
fungi and opposes the views of Dangeard. 
In a paper published in 1907 Clausen seems to have changed his 
views completely. He finds that the sexual organs of Pyronema 
confluens function, but nuclear fusion does not take place in the 
ascogonium. The male nuclei pass into the ascogonium, in the man¬ 
ner described by Harper, and a male nucleus pairs with a female 
nucleus but no fusion occurs. Conjugate divisions of the nuclei 
may occur as they migrate into the ascogenous hyphae. The ascus 
is formed in the manner described by Harper. The nuclei that fuse 
to form the primary ascus nucleus are, perhaps, direct descendants 
of the male nucleus on one side, and the female nucleus on the 
other, which paired in the ascogonium. 
Clausen (1908) states that sexual fusion occurs in Saproleginia 
monoica. Degeneration of all the nuclei of the oogonium except 
those at the periphery occurs. The peripheral nuclei divide mitoti- 
cally and from the daughter nuclei uninucleate eggs are formed. 
The antheridia apply themselves to the oogone, a pore is formed 
and nuclear fusion takes place between the male nucleus and the 
