Neo-Mendelism 69 



turn is the basis of evolution, has been emphasized 

 because its importance has perhaps not yet been suffi- 

 ciently appreciated. It promises to be one of the most 

 important theories of biology, which of course must be 

 tested by future investigation. 



The doctrine of cumulative factors was further 

 developed by East (i) in his work with corn. He was 

 able to explain some of the ratios obtained by assuming 

 three or four separately inherited cumulative factors, 

 just as Nilsson-Ehle had done. He obtained other 

 ratios, however, which required more independent 

 cumulative factors to explain. Some idea of the extent 

 of these investigations by East and his associates may 

 be obtained by noting the hst of the plant characters 

 whose inheritance they explained on the basis of cumu- 

 lative factors: number of rows, length of ear, diameter 

 of ear, weight of seed, breadth of seed, height of plant, 

 number of stalks per plant, earhness of flowering. In 

 all of these cases breeding gave the same characteristic 

 results. A cross between extreme parents gave hybrid 

 progeny intermediate as to the character in question; 

 and in the F2 generation the two extremes reappeared, 

 along with all gradations of intermediates. 



Nilsson-Ehle had been able to put his Fj inter- 

 mediates into definite classes, corresponding to the 

 number of doses of the determiner each had received. 

 East, however, could not do this with such exactness. 

 His results showed all gradations, but he could not 

 distinguish any definite groups; that is, gradation was 

 continuous and complete. In other words, he could 

 not tell with certainty from outward appearance just 

 how many doses of a given determiner an individual 



