Studies on Chromosomes 95 



times the female, sometimes the male, that has the larger number 

 and quantity. I therefore adhere to the view that if the primary 

 and essential difference between the two classes of spermatozoa 

 inhere in the chromosomes (there is of course room for difference 

 of opinion on this point) it must be, or originally have been, 

 qualitative in nature. 



Since the appearance of my third "Study," in which some general 

 discussion of the sex chromosomes was offered, there has appeared 

 an important paper by Correns ('07) on the higher plants, the 

 results of which, as he points out, harmonize remarkably with 

 those based on the cytological evidence. The most important 

 of his results is the experimental proof obtained by hybridizing 

 experiments on Bryonia, that in the dioecious species the pollen 

 grains are male producing and female producing in equal num- 

 bers, quite in accordance with the view put forward by McClung 

 ('02) in regard to the spermatozoa of insects and proved to be 

 correct in principle by the work of Stevens and myself. That the 

 same result should appear from investigations carried out on such 

 different material and by such different methods certainly gives 

 good ground for the belief that as far as the male is concerned 

 the phenomenon is at least a very general one. Professor Correns 

 points out in some detail the extraordinarily close parallel between 

 his experimental results and the cytological ones of Stevens and 

 myself; but the interpretation that he offers differs materially 

 from both those that I suggested in an analysis of my observa- 

 tions (Wilson '06). According to my first interpretation (Castle's) 

 both sexes are assumed to be sex hybrids or heterozygotes. The 

 conclusion of Correns is that, in respect to the active sexual ten- 

 dencies of the gametes that produce them, only the male is a sex 

 hybrid or heterozygote (d 1 (?)), while the female is a homozy- 

 gote (9 9). 14 This interpretation explains the numerical equality 



this is merely a casual fluctuation, the general rule being equality. This variation appears in dif- 

 ferent cells of the same cyst (as may be seen with especial clearness in the m-chromosomes in side 

 views of the second division where errors due to foreshortening may be eliminated). It would be 

 indeed strange if these relations were subject to no variation whatever. 



14 It is necessary to an understanding of Correns's view to bear in mind that the gametes are not 

 considered to be "pure" in the original Mendelian sense, but to bear both sexual possibilities, one of 

 which is "active," the other "latent." 



