Frey—Physiology of Venturia Inequalis. 
325 
From the literature reviewed one obtains no definite or uni¬ 
formly accepted ideas of the phytogeny or cytology of the ascomy- 
cetes. The followers of de Bary have not succeeded in establishing 
his views beyond dispute. Harper’s ideas are in line with those of 
de Bary and opposed to those of Brefeld and Dangeard. Clausen 
agrees with Harper except as to the fusion in the ascogonium. 
Fraser and Welsford, and Blackman and Welsford have taken a 
middle ground. On the one hand they resurrect the ideas of Bre¬ 
feld as to the function of the sex organs. They agree that two 
nuclear fusions occur and describe the three divisions in the ascus. 
The difficulty of following nuclear behavior and the development 
of the sex organs may be the reason for much disagreement. A 
large number of forms have been studied, but it is possible that 
we have only begun the cytological work. The work of Harper 
indicates the complexity of the problem. 
If we accept the views of Clausen it must be only upon incon¬ 
trovertible evidence as the double fusion, if it occurs, may be con¬ 
sidered an attempt in evolution which not other plants have under¬ 
taken. It would simplify the matter greatly to find that only one 
nuclear fusion occurred in the life history of the Ascomycetes, but 
mere simplicity should not mislead us nor prevent us from accept¬ 
ing conditions as they exist. 
The divisions in the ascus have been studied in great detail by 
Harper (1905) and Fraser and Welsford (1909). Only a small 
number of forms have been studied and more research may bring 
out many more interesting phases. In some of the yeasts and lower 
Ascomycetes only two divisions in the ascus are recorded whereas 
in Thecotheus ,(Overton 1906), Ehyparobius, (Barker 1905), and 
Ascoholus immersus, (Ramlow 1914), four and five divisions of 
the primary ascus nuclei may take place. 
De Bary’s idea that the sex organs of the fungi are functional 
becomes more plausible as cytological evidence accumulates in re¬ 
gard to the life history of the Lichens and Florideae. The law 
of function in a structure so important as the sex organs can only 
be viewed as due to a long cycle of evolutionary changes, to nutri¬ 
tional disturbances or to a sudden mutation. Paleobotanical 
studies indicate that the sex organs suffer little change through 
long cycles of time, whereas the vegetative organs may respond 
quickly to new environmental influences. Loss of function or 
suppression of an organ can scarcely be explained by the meager 
knowledge of physiology at our disposal. Such changes may be 
