294 Cardiff : Synapsis and reduction 



From the fact that in sections of close synaptic knots the threads 

 still show their bivalent character, the identity of the individual 

 threads probably is not lost in synapsis ; i. e., there is not a com- 

 plete intermingling of chromatic substance in the bivalent thread. 



The thread splits longitudinally in the first mitosis, probably 

 along the line of previous fusion. 



All of the chromosomes, at least in some "species, do not 

 behave alike in the reduction divisions. 



Considerable difference is found in the size of different chromo- 

 somes in the same species. 



Synapsis is probably the end-result of fertilization and a stage 

 of great chemotactic activity. 



Conclusion 



From the foregoing results it will be seen that there is con- 

 siderable uniformity in the behavior of the chromatin in the reduc- 

 tion phases of the forms studied. The results are largely in accord 

 with those of Allen ('05) and Berghs ('04), though they differ to 

 this extent, that there was observed no constant and definite stage 

 that could be called a second contraction period, and there was 



■ 



rarely found any opening out of the moieties of the bivalent spireme 

 after they had once joined. However, in Acer (figures 16-33), 

 and several of the other forms which are not included in this paper, 

 there is a slight separation of the moieties after the formation of the 

 heterotypic chromosomes, which is partly due, no doubt, to the 

 twisting of the chromosome as it is being pulled into the metaphase. 

 From the results obtained it seems highly probable that with 

 the fusion of the gametes in fertilization there is a nuclear but not 

 a chromatin fusion and that the maternal and paternal chromatin 

 retain their identity throughout the sporophytic existence of the 

 plant, finally fusing, in so far as it fuses at all, in synapsis. That 

 is, the sporophyte is a sort of double-celled phase of the organism. 

 Thus Cook and Swingle ('05), in an interesting article, argue that 

 the sporophyte is not an asexual but a highly sexual generation 

 or phase, in that it is produced " during the actual process of con- 

 jugation. " These writers hold that u it was not the reduction to 

 fewer chromosomes, but the retention of the double number, that 

 constituted the important step in sexual reproduction and made 



