192 Darling : Sex in dioecious plants 



if there was an essential difference in the character of the chro- 

 matin. I suspected at first that it might be due to an extra chro- 

 mosome, but further study showed that each nucleus contained 

 the same number. It is not impossible, however, that there may- 

 be two series of chromosomes that are inherently different in char- 

 acter and which are, therefore, handled differently in the recon- 

 struction of the nuclei. On the other hand, I find Wager ('04) 

 states that in the vegetative cells of Phaseolus the nucleoli origi- 

 nate by the fusion of the chromosomes, first into a number of 

 small nucleolar masses and then by further fusion into the large 

 nucleoli found in the mature cell. Some of his figures seem to 

 indicate that the fusion of these bodies does not take place at the 

 same time in each daughter nucleus ; and from an examination of 

 figures of other works this feature does not appear to be uncom- 

 mon. In view of these facts, It is impossible to judge how much 

 weight should be attached to this behavior of the chromatin in the 

 spore formation of this dioecious species ; but the fact that it occurs 

 so regularly in the great majority of cases during the early stages 

 of reconstruction, leads one to believe that it may not be without 

 significance. Considering the experimental work of Correns, it is 

 very tempting to conclude that this may have something to do 

 with the determination of the two kinds of pollen spores ; how- 

 ever, we can hardly be justified in drawing any conclusion. 



Coming now to the consideration of dioeciousness, the facts 

 point very strongly to the conclusion that in the dioecious mosses, 

 and probably in the dioecious Bryophyta generally, there is a 

 dominancy and a separation of the tendencies in the formation of 

 the spores. Evidently there is no such separation in the spore 

 formation of hermaphrodite mosses ; each spore must possess 

 both tendencies. One of the tendencies, however, must dominate 

 the other at some time during the germination of the spore pre- 

 vious to the formation of the sex organs. It does not seem in- 

 conceivable that this dominancy may take place in the vegetative 

 cell, possibly due to external factors or conditions ; this seems to 

 be evidenced by the work of Prantl, Klebs, and others on various 

 groups. Marchals* work clearly shows that fertilization brings 

 both tendencies together, making the sporophyte tissue bisexual 

 in character. By means of the protonemata regenerated from this 



