396 Harper — Sexual Reproduction in Pyronema 
out the possibility that reduction may occur in the ascus, the 
threefold division of the ascus-nucleus being possibly homo¬ 
logous with the double divisions of the spore mother-cells in 
the higher plants ; but the simultaneous divisions just prior 
to the formation of the ascus with the production, in some 
cases at least, of two nuclei which develop no further, suggest 
the possibility that reduction may occur at this stage. It is 
quite possible that the stages in development here are not to 
be homologized with those in the higher plants where a definite 
alternation of generations occurs ; still the ascocarp certainly 
plays the same role physiologically as the sporophyte of the 
higher plants, and the morphological equivalence of the struc¬ 
tures concerned is at least strongly suggested. From this 
standpoint reduction might occur at either of the stages 
mentioned above. Further study of the chromosome number 
in various forms among the thallophytes is necessary before 
a definite conclusion can be reached on this point. 
Madison, Wisconsin, May 22, 1900. 
