1920] 



CIIA M BERLA1 N—B0TRYCI1 1 1 .1/ 



397 



It would be interesting to compare the reduction divisions of 

 the two species, but the problem of getting material of B. dis- 

 sectum makes such a comparison difficult, if not impossible. Even 

 with good preparations of critical stages, the interpretation might 

 be uncertain, for, judging by a few figures in /->'. obliquum, the 2X 

 number is well over 100, and the 

 chromosomes are tangled and hard 

 to count. 



Such evidence as we have would 

 indicate that B. dissectum is at least 

 partially, and probably entirely, 

 sterile. Unfortunately the natural 

 test which would prove or disprove 

 this theory — germinating the 

 spores — cannot be applied until 

 someone learns how to make these 

 baffling spores germinate. If the 

 spores of B. dissectum germinate, 

 we do not see why this species 

 should not occur in groups, like 

 B. virginianum, B. obliquum, B. sim- 

 plex, and probably the other species. 

 In our opinion, the explanation 

 of the occurrence and behavior of 

 B. dissectum is that the species is 

 a sterile mutant from B. obliquum. 

 The principal facts supporting this 

 theory are that B. dissectum, so far 

 as I have observed in a five years' 



Figs. 10, 11. — Abortive spor- 

 angium of B. dissectum, with many- 

 layered wall and mass of mucilage 

 lining cavity from which sporogenous 

 tissue has been resorbed; X160: por- 

 tion of sporangium of B. dissectum, 

 showing spores of different sizes; 

 triangular spore doubtless abortive; 

 X350. 



study, never occurs except in asso- 

 ciation with B. obliquum, and that there is no evidence that it 

 reproduces itself. 



It might be objected that mutants do not occur so frequently 

 as B. dissectum would indicate, and it must be admitted that the 

 total number of plants in our plots is not as large as one might 

 wish in making ratios. The total number of plants in the twenty- 

 four plots was 482 of B. obliquum and 19 of B. dissectum, a ratio 



