116 THE SHORTER SCIENTIFIC PAPERS 



been recognized that hybrids usually grew to a larger 

 size than either parental form, as has been observed by 

 Kohlreuter ('63), Knight {'99), Gartner ('49), as well 

 as Darwin, Mendel and others, although the cause of the 

 increased growth has been purely conjectural. It is quite 

 evident that the result is due to either the increased num- 

 ber of cells, a suggestion made by East, to the increased 

 size of the cells, or to the combination of both conditions. 



The question immediately arises as to the cause of the 

 increased size and vigor among cross-bred multicellular 

 organisms when the evidence indicates that cross-bred 

 unicellular organisms are smaller instead of larger. Some 

 investigations in progress^ 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 better 

 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. 



3. 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, it may be noted that 

 the group containing close-bred, asexual or non-conju- 

 gating organisms, is more highly correlated in respect to 

 characters than the group consisting of cross-bred, sexual, 



^Walton, ('14). 



