Sex Determination 189 



nitely connected with sex determination, but the situa- 

 tion is most suggestive. 



The sex chromosome theory cannot apply, of course, 

 to the monoecious Uverworts, where the sexes must be 

 separated at a much later period than the reduction 

 division. In these cases obviously every spore contains 

 the potentialities for both sexes, and the two are sepa- 

 rated in connection with some of the vegetative divisions 

 of the bisexual gametophyte. In some species of 

 Riccia we know that a developing gametophyte pro- 

 duces only antheridia for a time and at a later period 

 produces archegonia only. The structural basis of this 

 change is not known nor the exact point at which it 

 occurs. 



Mosses. — A single very significant piece of work 

 by Marchal (9) will be mentioned. Funaria is a 

 dioecious moss, and hence it may be assumed that the 

 sexes are separated at the reduction division in the 

 formation of spores. Each spore carries the potentiali- 

 ties for one sex only; but of course the sporophyte as 

 a whole before the reduction division must carry the 

 potentialities for both sexes. Marchal, by a peculiar 

 technique of his own, cUpped a fragment from a young 

 sporophyte and induced it to reproduce aposporously; 

 that is, the sporophyte fragment produced a gameto- 

 phyte directly. The fragment must have contained the 

 potentialities for both sexes, since it consisted of tissue 

 in which reduction division had not yet occurred. 

 Logically the gametophyte should be bisexual, pro- 

 ducing both antheridia and archegonia, and this was the 

 result obtained. It is quite in accord with the sex 

 chromosome theory and is a striking confirmation of it. 



