No. 584] 



HEREDITY AND ITS MEANING 



463 



other animals, is a clear case of constancy in appearance. 

 In plants the same phenomenon has been observed. Eo- 

 senberg investigated the pollen mother cells of Crepis 

 virens and in certain stages in division invariably found 

 two long, two intermediate and two very short chromo- 

 somes. Division figures in the somatic cells showed the 

 same differentiation, and in an examination of the nuclei 

 of the pollen grain he found only one chromosome of each 

 kind present. Such other species of this genus as have 

 been investigated also show some variation in chromo- 

 some form, although it is not so striking as in C. virens. 

 Hicracium renosum, exceptionally good material also in- 

 vestigated by Eosenberg, has shown the same thing. 

 Edith Hyde remarks on the fact of the constant reappear- 

 ance of certain chromosome forms among hundreds of 

 division figures which she observed in Hyacinthus orien- 

 talis. Sauer mentions a very long chromosome constantly 

 present in pollen mother cell preparations of the lily-of- 

 the-valley, and Strasburger and Lutz found a large 

 chromosome among many small ones in Lychnis dioica. 

 In certain species of Yucca this chromosome differentia- 

 tion takes on a dimorphic aspect, ten of the chromosomes 

 being very large and about forty-five very small. 



Taking into consideration all of these facts, of which 

 hardly more than a random sample has been given, one 

 is clearly justified in concluding that these cell characters 

 are reproduced generation after generation. Why this 

 constancy if they are not important ? 



Physiological Individuality of the Chromosomes 

 There is also considerable reason for believing that the 

 various chromosomes of a cell may have different func- 

 tions. 



Boveri was the first to endeavor to test this hypothesis 

 by allowing sea-urchin's eggs to be fertilized by two sper- 

 matozoa. Three nuclei, each with eighteen chromosomes, 

 were thus present in the same egg, two male and one 

 female. Although cytoplasmic division seemed to pro- 



