580 THE AMERICAN NATURALIST. [Vol. XXXIX. 



Rosenberg's (:04a, :04b) studies on hybrids of Drosera rotun- 

 difolia (with ten chromosomes in the gametophyte) and D. longi- 

 folia (with twenty chromosomes) offer clear evidence that the 

 chromosomes which unite in pairs to form bivalent structures 

 preliminary to the reduction phenomena of sporogenesis are of 

 different parentage. The sporophyte number of chromosomes 

 in the hybrid is thirty, as would be expected. The reduced 

 number appearing at the first mitosis of sporogenesis is, however, 

 not fifteen but twenty chromosomes, ten of which are plainly 

 double the size of the other ten. The explanation of this inter- 

 esting condition is that the ten chromosomes of D. rotundifolia 

 unite with one half of the twenty chromosomes of D. longifolia 

 giving ten large bivalent structures accompanied by the ten 

 chromosomes of D. longifolia which are without mates. This 

 explanation finds clear support in the facts that the chromo- 

 somes of D. rotundifolia are larger than those of D. longifolia 

 and that the bivalent structure consists of a larger and a smaller 

 element thus giving clear evidence that the pairs of chromosomes 

 which unite in Drosera are of different parentage. The single 

 chromosomes which are without mates may pass to one or the 

 other of the poles of the spindle or may be left behind when the 

 daughter nuclei are formed. 



This group of investigations illustrates very clearly the charac- 

 ter of the evidence that is leading many biologists to assign to 

 the chromosomes the functions of bearing and distributing hered- 

 itary characters. The question at once comes up as to whether 

 or not the chromosomes may differ among themselves to a 

 greater or less extent even in the same species or individual. 

 Montgomery, Sutton, with others, have established a difference 

 in the size of chromosomes. Baumgartner distinguishes differ- 

 ences inform in the same species and the studies of Moenkhaus 

 and Rosenberg have shown that the chromosomes of different 

 parents may retain their peculiarities of form in hybrids and be 

 really separated. To these investigations should be added the 

 recent conclusions of Boveri ( : 02, : 04), that chromosomes actu- 

 ally differ in function. Boveri found that the chromosomes of 

 eggs of echinoderms that were fertilized by two or more sperms 

 are distributed by multipolar spindles to a varying number of 



