56 MITOSIS : THE VARIATION OF THE CHROMOSOMES 



of hydrogen-ion concentration on living chromosomes (Kuwada and 

 Sakamura, 1926), and are probably to be ascribed to differences of 

 dispersion of the permanent materials (genes) in the resting nucleus 

 and in the chromosomes rather than to a different degree of 

 proliferation of these materials. 



Cases which appeared to suggest the proliferation of permanent 

 materials and to clash with the principle of genotypic control have 

 been described by Tischler (1927) in Ribes and by Skovsted (1929, 

 1934) in '^scttlus and Gossypium. A distinction between the large 

 chromosomes of one species and the uniformly smaller chromosomes 

 of another species (a distinction such as could hardly be due to 



Table 5 

 Lengths of Chromosomes in Species and their Hybrids 



Structural change) was found to be retained in the hybrid. These 

 descriptions have not been confirmed (D., 1929 « ; Upcott, 1936 h). 



(ii) Chromosome Spiralisation. (a) Phragmatohia fuliginosa 

 occurs in two races, one with constantly greater linear contraction, 

 and greater width of chromatid than the other at mitosis, and at 

 meiosis (Seller, 1925). 



(6) Two individuals of Melandrium album have been found to 

 have chromosomes constantly about one-third the normal length. 

 They therefore resembled the normal meiotic chromosomes in shape 

 (Breslawetz, 1929). 



(c) In the third generation from the cross Viola tricolor by 

 V. Orphanidis, a segregate appeared having longer and thinner 

 chromosomes than the parental species, or indeed any other 

 species, of Viola. This reduced contraction is correspondingly 

 effective at both meiotic divisions. It must be contrasted with the 



