No. 5S7] 



VARIABILITY AND AMPHIMIXIS 



677 



Some investigations in progress 3 suggest an answer 

 meeting the conditions, although more than a provisional 

 opinion may as yet not be ventured. This is to the effect 

 that the cells of cross-bred multicellular organisms are 

 actually smaller than the cells of pure line or inbred 

 organisms, and that the more rapid division is a function 

 of the greater ratio surface has to volume in a small cell 

 with the bettor opportunity this afforded for an increased 

 metabolism. 



The increase of size in plant and animal forms to the 

 physiological limit has great importance for the future 

 of agriculture and stock breeding, but many subsidiary 

 problems must be solved before practical results are at- 

 tained in this direction. The relative rate of growth, 

 number and size of the constituent cells of pure line and 

 of hybrid individuals is one of the problems. 



5. Comparative Correlation Resulting from Close 

 Breeding and Cross Breeding 



The close-bred zygospores are more correlated as to 

 length and diameter than the cross-bred zygospores, but 

 since the difference only slightly exceeds twice the prob- 

 able error, the value of the result here is questionable. 

 Considering other investigations (Table XII), it may be 

 noted that the group containing close-bred, asexual or 

 non-conjugating organisms, is more highly correlated in 

 respect to characters than the group consisting of cross- 

 bred, sexual, or conjugating organisms, although two 

 exceptions, No. 12 and No. 14, are presented. An in- 

 teresting fact, although possibly only a coincidence, is 

 that cross bred zygospores of Spirogyra and of conjugat- 

 ing Paramecium have approximately only one half the 

 correlation exhibited by close bred zygospores of Spiro- 

 gyra and by non-conjugating Paramecium. 



The explanation of the conclusion here reached, that 

 the value of a character "x" in cross-bred forms does 

 not have the same tendency to change that the value of a 



