762 



INHERITANCE 



Effect of the Cytoplasm and Its Relation to 

 Nuclear Constitution 



Certain phenomena in the biparental reproduction of ciliates throw 

 hght on the relative role of the nucleus and the cytoplasm in inheritance. 

 Such phenomena are shown in the inheritance of a number of different 

 types of characteristics, but are best seen in crosses of individuals of 

 different inherited sizes, as set forth in the work of De Garis (1935) . 



By ingenious methods De Garis obtained in Paramecium caudatum 



Figure 176. Change of size resulting 

 from conjugation of individuals of large 

 and small races, in the experiments of 

 De Garis. Upper left, A and B, the 

 large and small individuals of the pair, 

 showing their relative sizes. The columns 

 headed A and B respectively show (read- 

 ing from above downward) the average 

 sizes of the descendants of the two at 

 successive intervals of two days each. 

 (Diagram based on the measurements of 

 De Garis, 1935.) 



conjugation between races the members of which differed greatly in size. 

 The nature of the consequences will best be seen from a typical example. 



In a certain case one of the members of a pair (A, Fig. 176) belonged 

 to a race in which the average length of the individuals was 198 microns, 

 while the other belonged to a small race with an average length of but 

 73 microns (B, Fig. 176). The large individual of the pair had thus 

 about twenty times the bulk of the smaller one. 



Before conjugation the large and the small sizes are inherited in the 

 two races; all individuals of race A are large, all those of race B are small. 

 The two individuals of the different races conjugate and exchange a 

 haploid set of chromosomes, then separate. The two are now alike in 

 their nuclei, but are diverse in their cytoplasm — one having the cytoplasm 

 of race A, the other that of race B. The ex-conjugant A still has the 

 large size of race A, the ex-conjugant B the small size of race B. 



