52 



THE CELL AND PROTOPLASM 



for many generations, but finally the de- 

 scendants of the two parents come to a 

 common size, corresponding to the proper- 

 ties of the common nuclear constitution. 

 The final size is, however, not always mid- 

 way between the sizes of the two parents. 

 Such a case is illustrated in Fig. 2; in 

 which the final size reached by both sets 



Fig. 2. Paramecium caudatum. Changes in size 

 resulting from the crossing of two other races dif- 

 fering in size (these races are again designated A 

 and B). At the upper left are shown the relative 

 sizes of A and B immediately after conjugation. 

 The sizes of the two clones at the end of successive 

 two-day periods are shown, reading from left to 

 right in the three rows, beginning with the top row. 

 Finally (lower right) the descendants of the two 

 ex-con jugants reach a common size which is near 

 to that of the parent B. Drawn to scale from the 

 dimensions and curves given by De Garis (1935). 



of descendants is near that of the smaller 

 parent. What the ultimate size shall be 

 obviously depends on what nuclear com- 

 bination is present in the two parents after 

 conjugation. 



One other set of facts may be mentioned 

 briefly. When many crosses are made be- 

 tween the same two clones or races, the final 

 size reached by the descendants is not neces- 



sarily the same in different cases. Differ- 

 ent pairs of the same cross — the two par- 

 ents having the same genetic constitution 

 in each case — ^yield descendants of very 

 different final sizes. These relations are 

 illustrated in Fig. 3, which represents to 

 scale the results of several different crosses 

 made by De Garis. It is clear that in dif- 



12 3 4 



I 2 3 



12 3 4 



I 2 3 



Fig. 3. Diverse final sizes resulting from different 

 pairs in crosses of particular races. The results of 

 four diverse crosses are shown (in each cross the 

 parent races are designated A and B), In the first 

 two crosses the final sizes are shown for four dif- 

 ferent pairs: they are designated 1, 2, 3, and 4. 

 In the third and fourth crosses the final size is 

 shown for but uhree pairs (1, 2, 3). Drawn to 

 scale from the dimensions and curves given by De 

 Garis (1935). 



ferent crosses of the two races, different 

 combinations of chromosomal materials are 

 made, resulting in descendants of different 

 final sizes. The phenomena are of the 

 same kind as those seen in the fact that 

 children of the same human family differ 

 in their inherited characteristics. 



Return now to the relations of nucleus 



