PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE 127 



plant forms in particular usually grew to a larger size than 

 either parental form, a result undoubtedly due to the 

 greater rapidity of cell division and consequently greater 

 number of cells as conjectured by East. In the study of 

 zygospores of Spirogyra it was therefore noticed with some 

 interest that the cross bred forms were smaller than the 

 close bred forms both so far as length and volume were 

 concerned. Jennings (1911) in his study of Paramecium 

 reached a contrary conclusion, stating that "The progeny 

 of conjugants * * * were a little larger than the prog- 

 eny of non-con jugants and the difference appears to be 

 significant." This is correct merely in reference to length, 

 however, and that it is not true for actual size as indicated 

 bj^ volume is evident on applying the formula for the volume 

 of a prolate spheroid (V = 1-6 nld-) by which it may be 

 demonstrated that the non-con jugant forms, while smaller 

 than the others at the beginning of the experiment, actually 

 became larger. Thus in agreement with the zygospores of 

 Spirogyra, conjugation decreased size. 



The question immediately occurs as to the cause of the 

 increased size and vigor among cross bred multicellular 

 organisms when the evidence indicates that cross bred 

 unicellular forms are smaller instead of larger. 

 Some investigations that I have undertaken indicate an 

 answer apparently meeting the conditions. While suffi- 

 cient control experiments have not been made to venture 

 more than a provisional opinion, the data suggest that the 

 cells of cross bred multicellular organisms are actually 

 smaller than the cells of inbred or Pure Line forms, 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 thus obtained for increased metabolism. 



That there is need of farther investigation on size and 

 variability in pure lines and in cross bred forms through 

 the application of statistical methods in connection with the 

 maintenance of pedigree through long series of generations 



