394 Harper.—Sexual Reproduction in Pyronema 
condition of the Exoasci it is at least apparent that the 
absence of sexual apparatus in them cannot be regarded as 
evidence of the absence of sexuality in other more typical 
Ascomycetes. De Bary’s view that they are reduced and 
specialized forms is at least as well founded as the view that 
they are typical of the primitive Ascomycetes. Dangeard’s 
(7) view also, according to which the Exoasci furnish evidence 
of the sexual nature of the nuclear fusions in the ascus, cannot 
be regarded as conclusive, since I have shown that similar 
nuclear fusions occur in asci arising themselves from a ferti¬ 
lized egg in the Erysipheae and Pyronema. Until the method 
of spore-formation in the group has been worked out the 
question as to its position and relationships may be left entirely 
open. 
The significance of these nuclear fusions in the ascus is very 
obscure. Still the entire process in sexual cells and asci is 
not without analogy elsewhere. Chmielewski (6) has de¬ 
scribed the nuclear phenomena in the zygospore of Spirogyra 
as consisting of a nuclear fusion at the time of cell-conjugation 
followed by a double division of the fusion-nucleus, the dis¬ 
appearance of one pair of nuclei so produced, and the fusion 
of the other pair. Wager (40) has pointed out that this 
process seems somewhat similar to the series of nuclear 
phenomena in Sphaerotheca. The fertilization occurring in 
the oogonium would correspond to the first fusion in Spiro¬ 
gyra. The period of growth of the ascogonium is then 
interpolated, followed by a second fusion in the ascus corre¬ 
sponding to the second fusion in the zygospore. In Pyronema 
the same comparison can be made, and further, the disintegra¬ 
tion of the two nuclei in Spirogyra may be analogous to the 
cutting off of the two nuclei at least in some cases in the 
sterile cells at each side of the ascus-bearing cell ; but here 
again the apparent resemblance may have more or less 
morphological significance. 
We certainly need more light on the phenomena of chromo¬ 
some-reduction, and the method and time of its occurrence in 
the lower plants, before a conclusion can be reached on this 
