NUCLEAR FUSION IN THE ASCUS. TZ 



plants, since both contain the double number of chromosomes. While 

 this is possible, I doubt if the evidence proves quite so much. The 

 tendency certainly exists among the most recent students of reducing 

 phenomena, accepting the suggestions of De Vries (96) and still earlier 

 evidence from the side of the zoologists (65, 66), to assume that the 

 entire interchange of hereditary units or of hereditary influences between 

 male and female chromosomes takes place in synapsis or the associated 

 stages. With this view it is a matter of indifference, as Blackman main- 

 tains, whether the nuclei of the gametes combine into one early or late 

 in the life of the sporophyte. One nucleus with the double number of 

 chromosomes is exactly the equivalent of two distinct nuclei which 

 divide by conjugate division. Still, it is to be questioned whether this 

 is actually the case physiologically. It may very well be that the male 

 and female chromosomes in the nuclei of the sporophyte of the higher 

 plants, though maintaining their individuality as permanent structures, 

 can still exert chemical or other influences upon each other in some 

 degree as a result of their close association in the same nuclear cavity, 

 whether or not an actual interchange of substance occurs between them. 

 The facts of bud variation, adaptation to environment, and other modi- 

 fications occurring during the life of the individual suggest that this 

 may be the case. If such interchange takes place in a fusion-nucleus 

 and does not occur in a binucleated cell arising from conjugate division, 

 then the fusion in the teleutospore may mean more than the reduction 

 process found in the spore mother cells. A result which is achieved 

 immediately in the union of the nuclei of the sperm and t^'g, or later 

 during the association of the male and female chromosomes in the sporo- 

 ph3rte, may here be accomplished at the stage of chromosome reduction. 

 It may be that the nuclear fusion everywhere means more than a mere 

 preliminary adjustment making ready for reduction. I am inclined to 

 think that this is the case and that the fusion in the teleutospore may 

 involve in some degree the changes resulting from sexual union beyond 

 those which arise from such a cytoplasmic fusion as results in the binu- 

 cleated cell, as described by Blackman and Christman. 



The question further arises, granting that this difference between 

 reduction phenomena in spore mother cells and the processes in the 

 teleutospore exists, whether it is of such a nature as to replace in any 

 degree, when the nuclei which fuse come from a separated ancestry, 

 the ordinary sexual conjugation of cells and nuclei as they are found 

 elsewhere in algs and fungi. There seems no doubt, in view of Miss 

 Nichols's (71) results, that in certain Basidiomycetes the origin of the 

 binucleated cells is not found in any such definite structures or at any 



