5° BOTANICAL GAZETTE [JULY 
not through lack of time, therefore, that one would suggest that 
it is unlikely for a leafy sporophyte to have been developed from 
a sporogonium. From the fact that our earliest evidences of the 
pteridophytes show them to have been about as highly differ- 
entiated as they are now, it is evident that the evolution of the 
line reaches very far back. It is probably hopeless to expect 
that this gap in our knowledge will be filled. 
The other gap is in reference to cytological details. The 
whole subject of alternation of generations seems to be s0 
bound up with nuclear changes that a knowledge of these it 
the thallophytes becomes a very great desideratum. This gap 
in our knowledge is likely to be filled up rapidly. It may be 
that we have been too rigid in our use of the number relations 
of chromosomes as distinguishing gametophytes from sporo- 
phytes. Be this as it may, there is enough in the testimony 
associating the doubling and the reduction of chromosomes 
with the sporophyte and gametophyte stages to justify such use. 
It would seem that an investigation into the nuclear changes 
which occur in the “fruit bodies” of such forms as CEdogonium 
and Coleochete would go far toward settling the antithetic origin 
of such a structure at least as the sporogonium of bryophytes 
It is not my purpose in this paper to traverse ground which 
has been gone over so recently and so ably, but merely to dis- 
cuss certain facts and possibilities in connection with the leafy 
sporophyte that may be suggestive. In discussing the origin of 
such a structure as the leafy sporophyte where there is 1° 
possible direct evidence, and where every view must be hypothet- 
ical 
coordinate the facts and to suggest lines of research. 
No structure among plants seems to have left so little trace 
of its origin as the leafy sporophyte of pteridophytes and 
Spermatophytes. The evolution of the leafless sporophyte : 
bryophytes seems traceable from an oospore which directly 
organizes a group of sporogenous cells. Sterilization of the 
peripheral cells would result in a simple spore-case like that of 
» It seems necessary to consider all possible alternatives: 
The chief service which these various alternatives render is 0 
