218 BOTANICAL GAZETTE [Marcu 
The questions involved in the study of the nuclear history of 
the Ascomycetes will never be satisfactorily answered by a priori 
argument. The careful examination of a large number of repre- 
sentatives of ‘this group presenting peculiarly favorable material for 
investigation, and the comparison of the data obtained with those 
available for other groups will, however, go far toward explaining 
the discrepancies in conflicting accounts and toward answering 
vexing questions to the satisfaction of all students. 
The greatest variation is evident in the morphology of the sexual 
apparatus in the Ascomycetes even in forms in which the gross 
structural characters of the ascocarp are very similar. The pub- 
lished evidence would seem to show, moreover, that a certain 
amount of variation in the unfolding of the sexual phenomena 
may be encountered in the investigation of even a single species. 
In Pyronema confluens the sexual phenomena have been vari- 
ously described. Harper (40) gives in detail the passage of the 
male nuclei from the antheridium into the ascogonium, their 
fusion there in pairs with the female nuclei, the migration of the 
fusion nuclei into the ascogenous hyphae, and later a second fusion 
in the ascus. CLAUSSEN (16, 17) also describes the entrance of 
the antheridial nuclei into the ascogonium, but states that they 
merely pair there with the female nuclei without fusion. These 
pairs of nuclei then migrate into the ascogenous hyphae where they 
divide conjugately, two nuclei ultimately fusing in the ascus to 
give a fusion nucleus with the diploid number of chromosomes. 
This demonstration by CLAUSSsEN of conjugate divisions in the 
ascogenous hyphae is especially noteworthy, since these divisions 
in the undifferentiated portions of the hyphae have not been 
demonstrated elsewhere in the Discomycetes. Since these nuclei 
divide conjugately, there is good reason to feel that they are linked 
together by a sexual attraction. FRASER (30), however, says that 
“the phenomenon of conjugate division is probably but a special 
exainple of the very general fact that nuclei present in the same cell 
usually divide simultaneously” (FROMME 34, OLIVE 55). WELSFORD 
(66) suggests that the paired condition of the nuclei may be merely 
the response to the physiological conditions usually found in rapidly 
developing hyphae. VAN TreGHEM (62) grew under cultural con- 
