ALTERNATION OF GENERATIONS. 79 



condition arises in the sporidium or later in the growth of the mycelium. 

 Still, no claim for completeness was made, since we did not germinate 

 the sporidia nor determine the nature of the early stages of the mycelium 

 which arises from them. As to the question of a name for the fungus, 

 in the absence of definite evidence it is, in my opinion, poor policy to 

 reject this commonly used name (24) until by culture experiments posi- 

 tive proof of its identity and relationships has been attained. The main 

 conclusions reached in the paper in question were that much more differ- 

 entiated and normal division figures were present in the rusts than had 

 up to that time been described, and especially that the then current 

 conceptions as to the number of chromosomes in the nuclei of the rusts 

 were entirely wrong. In both of these points Blackman's results con- 

 firm our own. 



If, further, as Blackman believes, the rusts may have arisen from 

 the Florideae, it is probable that, at a time when the spermatia were the 

 functional male cells, there was a fusion of nuclei immediately in the 

 fertilized cell. If, at this stage in the development of the group, a 

 sporophyte generation leading to the formation of such spore mother 

 cells as the basidium were in existence, it is not improbable that two 

 nuclear fusions may have been included in such a life cycle. On the 

 other hand, from this standpoint alone the opposite conception that the 

 various spore forms of the rust arose gradually in connection with a 

 progressive deferring of the fusion of the nuclei of the gametes seems 

 also plausible. There are, however, other facts to be taken into con- 

 sideration. 



ALTERNATION OF GENERATIONS IN THE HIGHER FUNGI. 



It seems entirely clear, from our knowledge of the significance of 

 the chromosome number in nuclear division, in sexual reproduction, 

 and in the alternation of generations in the higher plants, that the deter- 

 mination of the number of the chromosomes at the important stages 

 in the life cycles of the higher fungi will indicate definitely the true 

 nature of the difficult phenomena we are considering, and there is no 

 doubt that the problem is soluble along these lines. We have abundant 

 evidence that in the asci the chromosomes are very sharply differentiated 

 structures, which can be counted with certainty. It is certain that, as 

 shown above, the nuclear fusion in the ascus does not alter the apparent 

 number of the chromosomes found in the fusion nucleus and its off- 

 spring as compared with the individual nuclei which combined. The 

 fusion of the nuclei involves the union of the chromosomes presumably 

 in pairs, and thus, through synapsis and the triple division which follows, 



