The Spermatogenesis of IIvukid Peas 531 



nothing is clearer than the fact that the present conception of the 

 essential nature of the maturation processes in pure races of plants 

 does not provide adequate grounds for this variation. This study 

 v/ill hardly profess to do this, but I may repeat what I have be- 

 fore suggested * and what Montgomery f and Sutton | have em- 

 phasized, that a study of the early history of the reproductive 

 cells may give some clue leading to a better understanding of the 

 meaning of heterokinesis, and, at the same time, a truer concep- 

 tion of the physical basis for variations, both in pure races and in 

 hybrids. With this idea in mind I have studied, as well as the ma- 

 terial at hand would permit, the divisions of the sporogenous 

 cells, more especially the last one, the division preceding the first 

 maturation mitosis, in the hybrids and in the pure form Fillbasket, 

 and I have found unmistakable evidence of an association of the 

 chromosomes two and two. Of course I cannot say positively 

 that this was not a chance association, since I could not trace the 

 later phases of these divisions as closely as would have been de- 

 sirable, but the pairing was observed in well prepared material and 

 had every appearance of being the normal and regular occurrence. 

 If further studies confirm this observation, it may prove of great 

 importance in explaining the structure of the heterotype rings. 

 There are difficulties in the way of positively identifying any 

 chromatin loop as having its origin in any given pair of chro- 

 mosomes, because the nucleus enters on a complete resting stage 

 at the close of the presynaptic mitosis and the identity of the 

 chromosomes is lost. Further studies may, however, give re- 

 sults that point to a connection between the two even if they do 

 not make the demonstration. For example, I have seen the union 

 of chromosomes by the polar ends only, in the telophases of the 

 last sporogenous division, and I failed to find, although I searched 

 very closely, the formation of a spireme, but in the place of it the 

 pairs of chromosomes appeared to be united at the polar ends. A 

 continuous spireme may not be formed in this division. It is con- 

 ceivable therefore that the chromosome pairs which enter the rest- 

 ing condition may be identical pair for pair with the loops which 

 are formed later. 



* Cannon, 2. 



I Montgomery, /. c. 

 I Sutton, /. c. 



