546 WHITE— STUDIES OF INHERITANCE IN PISUM. 



Dzuarfs X dwarfs always gave dwarfs in F^ and succeeding 

 generations. 



Interpretation. 



The inheritance of height in peas is an extremely important 

 subject from a practical standpoint and well worth a most detailed 

 and thorough study. In most cases, data now obtainable are ex- 

 tremely fragmentary and too general in character. However, so 

 far as our present knowledge goes, two factors are involved and 

 according to Keeble and Pellew — one (T) determines stem thick- 

 ness, W'hile the other (Le) gives rise to long internodes. The com- 

 bination of TLe produces tails in F,^ and F2, while the absence of 

 these factors in F„ gives dwarfs with thin stems. Many dwarf 

 varieties have thick robust stems, though all known to me have 

 comparatively short internodes and only few in number. Hence 

 it seems to me that T stands not for thickness of stem but as a 

 factor for large number of internodes. Interpreted in this manner, 

 the formulas for various heights in pea varieties would be : 



Tall, large number of long internodes, TTLeLe, 

 Half dwarf, large number of short internodes, TTlele, 

 Half dwarf, small number of long internodes, ttLeLe, 

 Dwarf, small number of short internodes, ttlele. 



Both the interpretation of Keeble and Pellew as well as the one 

 just given fail to account for the usual results from crossing tails 

 and dwarfs. If tails are bifactorial in composition, in F,, instead 

 of tails and dwarfs being the only classes, half dwarfs should be 

 extremely common, w^hile dwarfs would appear not more than once 

 in every 16 segregates. However, the classification of F, popula- 

 tions involving tails and dwarfs has been based in all probability in 

 most cases on the length of the internodes, all segregates with long 

 internodes, regardless of number, having been classed as tails, while 

 those with short internodes were classed as dwarfs. In this way, 

 the usual 3 : i ratio would be obtained, as only the factor Le is in- 

 volved. The length of the internodes are shortened by the absence 

 of the factor Fa and increased in number. This explains the tails 

 with a large number of comparatively short internodes. As pointed 

 out by Bateson (i), the groups designated tails, half dwarfs and 



