^0 HORTICULTURAL SOCIETY OF NEW YORI^. 



tained its individuality, and was disposed in such a manner at the time of 

 the maturation mitoses that the resulting sex cells were not hybrid, but pure. 



A portion of this hypothesis has already been demonstrated to be true, 

 namely, in hybrid ascaris, the chromosomes derived from the variety bivalens 

 keep, separate from the one which is evidently from the nnivalens parent. 

 And it will appear presently that an analogous condition may obtain in other 

 hybrids. 



That a hybrid sex cell has chromatin of pure descent — that is, has chro- 

 matin from one parent only, as the second law of Mendel apparently de- 

 mands — is yet to be proved, and may be doubted on a priori grounds, since 

 the wall separating the daughter nuclei is laid down at right angles and not 

 parallel to the spindle of the dividing nucleus. However, if it can be shown 

 that the Pimm type of hybrid, for example, is associated with the general 

 behavior of the chromatin, as just suggested, a very important and forward 

 step in explanation of the nature of this and other types of hybrids shall 

 have been made. On the other hand, it will be quite as important to demon- 

 strate that variation in hybrids may take place, even if the sex cells are 

 formed in a manner identical with those in pure races. 



Now that I have pointed out the possible relation between the experi- 

 mental and the cytological study of hybrids, I hasten to say that, in reality, 

 up to the present moment there has been no such connection, since the cyto- 

 logical work was mainly completed before the experimental was published ; 

 and, further, since the forms which have been turned to account cytologically 

 have not been studied experimentally. With this I shall proceed to speak 

 briefly of the cytological work. 



This has comprised studies by Guyer on the spermatogenesis of hybrid 

 pigeons and c annas, by Juel on the spermatogenesis of hybrid Syringa, and by 

 the writer on spermatogenesis of hybrid cotton. In addition, the study on 

 Ascaris, already sufficiently alluded to, and also the structural study of sev- 

 eral hybrid plants by Macfarlane may be included here. 



Concerning all of the plants upon which cytological studies have been 

 made it may be said that they are first generation hybrids ; that is, they are 

 the offspring of the original cross. 



Guyer reports upon the spermatogenesis of hybrid pigeons, and also 

 cannas, but since the results are analogous and the conclusions identical I 

 need only outline the results of his study of the former. 



I understand that Guyer found in the pigeon normal and abnormal sper- 

 matozoa and normal and abnormal maturation mitoses. In the normal male 

 nuclei the first maturation division showed ring-formed chromosomes, of uni- 

 form size, and of half the somatic number. He found, on the other hand, in 

 the abnormal maturation mitoses that the ring-formed ciiromosomes might 

 be of two sorts, large and small, or they might all be small ; and if the latter, 

 they were the same number as those in the stomatic nuclei. In such abnormal 

 nuclei there was a tendency of the chromosomes to form into two groups, 

 and this localization was taken to indicate the maintenance by the chromo- 

 somes of their individuality. The general conclusion of the author was, that 

 the variation noted in the maturation mitoses was likely associated with the 

 variation of the hybrids themselves. 



