74 Plant Genetics 



factors cumulative in their operation; (2) the significance of the 

 breeding results is usually somewhat obscured by the natural 

 fluctuations due to response to uncontrollable factors in the 

 environment. 



Others have investigated the problem of cumulative 

 factors, and many of the results are favorable to the con- 

 ception; but much more investigation should be made, 

 for the conception deals with exceedingly fundamental 

 situations. If it is true it is extremely important; if it 

 is not true a knowledge of this fact is just as important. 

 It is like a fork of the roads in our biological progress; it 

 is important to know which is the right road for future 

 progress. 



In concluding the general topic of cumulative factors 

 a modifying statement should be made as to the mecha- 

 nism involved. Heretofore it has been assumed that we 

 were dealing with numerous, separately inherited factors, 

 absolutely identical in their nature, cumulative in their 

 effect. No doubt one might regard with suspicion such 

 a seemingly artificial mechanism. Probably it would 

 be easier to believe if it were modified in the follow- 

 ing manner. Instead of assuming numerous factors, 

 identical in function, we may assume that each of these 

 factors has its own peculiar function, but that that 

 function plays a part, directly or indirectly, in develop- 

 ing the quantitative character in question. For example, 

 suppose height is the character. One of the factors 

 determines the development of long internodes; another 

 results in numerous nodes; another increases the amount 

 of chlorophyll; another determines the size and vigor 

 of the root system; another brings early germination 

 and long growing season. Such factors, then, although 



