WHITE— STUDIES OF INHERITANCE IN PISUM 665 



well under ordinary conditions if they average four pods per vine, 

 while some of the late varieties with large vines may average 30 to 

 50 pods. Variation in the number of pods per single vine is large 

 even among the individuals of a pure varietal strain, but in some 

 cases this may be regarded as almost entirely environmental. Fur- 

 ther the extremes as to few or large number of pods never transcend 

 certain limits, and supposedly these limits represent the character 

 of the environment, whether most unfavorable or most favorable. 

 Olin (63) records a plant grown in the Colorado mountains under 

 exceptional conditions which was 3 meters high and bore 650 pods 

 averaging 5 peas per pod. On the other hand, some of the wnld 

 forms average 4 pods per plant. 



Hurst (44) grew 112 varieties under about the same conditions. 

 From data on these, the heaviest yielders appeared to be those varie- 

 ties with the largest number of pairs of pods, but he states this to 

 be more apparent than real. Some varieties generally bear pods 

 singly, while other varieties have them in pairs or in threes. Twenty 

 plants of Velocity gave Hurst 202 singles and no pairs, while a 

 score or more of plants of other varieties gave all the way from 4 

 doubles: 471 singles to 142 doubles : 593 singles. 



Shaw (70) from a large series of biometrical studies on sev- 

 eral pea varieties came to the conclusion that the number of pods 

 per single plant was not a heritable character, but that it was cor- 

 related with vine length, which is heritable. Shaw's experiments 

 and treatment of his material, however, were not of such a character 

 as to throw much light on this subject. Shaw and others point out 

 the probability that each node is potentially capable of producing 

 pods. In most modern studies of heredity, however, one considers 

 only the physical characteristics of a plant or a variety as they 

 actually are under a given set of environmental conditions and not 

 the potentialities or possible variations of this plant or variety under 

 a thousand and one environments in which it might be grown. 



The productivity of any variety of pea, as is well known, is in- 

 creased by harvesting the green marketable pods, instead of allow- 

 ing the first crop to mature. 



Relander (66) has begun a careful study of the problem of pro- 

 ductivity in peas by growing the parents and crosses in pots of 



