522 Cannon : Studies in Plant Hybrids : 



pairs are united in this manner a continuous spireme of single 

 chromosomes united end to end would be the result. The results 

 of my observations upon this point were somewhat contradictory^ 

 and this may have been owing to the possibility that not all of the 

 nuclei studied were undergoing the last sporogenous division, and 

 that the pairing of the chromosomes and the form of telophase fol- 

 lowing are, in the pea, peculiar to the presynaptic nuclear division. 

 I hope at another time to give a more complete account of this 

 division. 



When I observed the association of chromosomes as above de- 

 scribed I supposed that it was merely from chance, which indeed 

 may yet prove to be the case, and not the usual and normal occur- 

 rence in such cells, because it surely is not at all hkely that so no- 

 ticeable a thing could for any length of time escape the eyes of 

 trained cytologists. The better to reinforce the correctness of my 

 observation, or to prove it false as the case might be, I studied the 

 mitoses in the nuclei of somatic cells. As a rule, there is no indica- 

 tion whatever in the somatic nuclei of peas of the association of the 

 chromosomes in twos, but in one nucleus an appearance recalling 

 the pairing was observed. In this case a closer examination 

 showed that the association did not include all of the chromo- 

 somes and was very evidently one of chance merely ; so that it 

 seems to me that the association of the chromosomes in pairs in 

 the last sporogenous division in Fillbasket does not find a coun- 

 terpart in any somatic cells and is not the result of chance. 



Fillbasket x Debarbieux 



In studying the sporogeny of the hybrid Fillbasket x Debar- 

 bieux my aim has been rather to notice departures from the " nor- 

 mal," and by it to discover if possible the structural causes of the 

 remarkable " splitting " of the Mendelian hybrids, than to examine 

 critically and minutely the several nuclear divisions for themselves. 

 Accordingly I have observed the behavior of the chromosomes 

 more especially in the two maturation mitoses, in the first division 

 of the microspore and in the last division of the sporogenous cells. 



The sporogenous cells of the hybrids were rather easily dis- 

 tinguished even in young anthers because of their position and by 

 the greater density of the cytoplasm, although it should be said 



