172 Gardner — Studies on Grozvth and Cell 



According to this, Hertwig's first condition is assured, for 

 if chromatin alone were regarded as the bearer of hereditary 

 ■substances the equivalence cannot be retained. 



The second condition is likewise assured. The hereditary 

 mass being composed of nucleoli and chromatin, is equally 

 distributed, during karyokinesis, among the cells derived from 

 the fertilized ovum. 



Those who consider the chromatin to be the sole hereditary 

 ■substance believe that the elimination of hereditary substance, 

 which would be necessary to prevent a summation of the 

 hereditary masses, is effected by the so-called " division with 

 reduction." But this latter theory is not yet established on 

 a sure basis. 



The fourth condition affects Strasburger's nuclear hypothe- 

 sis and the proposed extension of it equally. 



Therefore, judged from Hertwig's criterion, this theory 

 regarding the chromatin and nucleolus, as hereditary in func- 

 tion, finds no objections. 



Mature tissues contain relatively a large amount of nucleolar 

 substance and a relatively small amount of chromatin. As 

 the cell becomes specialized, the chromatin is reduced in 

 quantity until the idioblasts representing the special properties 

 of the mature cell are alone present. 



The great surface of the chromatin as compared with the 

 small surface of the nucleolar substance favors the view that 

 chromatin may be composed of active idioblasts. The greatly 

 attenuated thread, described by Rosen, is explained readily by 

 this theory. This long chromatin thread is immersed in a 

 nuclear fluid containing a large amount of nucleolar substance 

 suspended in it, and thus a uniform distribution of idioblasts 

 along this thread is possible. The persisting portion of the 

 nucleolus contains that portion of hereditary substance which 

 is to be got rid of and not to appear in succeeding generations. 



The transformation of the nucleoli, bodily into nuclei, in 



