INHERITANCE STUDIES IN PISUM. IV. INTERRELATION OF 
THE GENETIC FACTORS OF PISUM 
By Oreand E. White, 
Curator of Plant Breeding, Brooklyn Botanic Garden; Collaborator, Office of Forage 
Crop Investigations and Office of Horticultural and Porno logical Investigations, Bureau 
of Plant Industry, United States Department of Agriculture 
INTRODUCTION 
The present paper describes and discusses the number of demonstrated 
factors in Pisum, their modifying effects upon each other's expression, the 
modification of their expression by different environments, and their rela¬ 
tion to one another in inheritance, whether independent or linked. 
MATERIAL, AND METHODS 
As pointed out by Mendel, Correns, Lock, and many others, the pea 
plant is in many respects especially favorable material for studying such 
genetic problems as these because of the ease with which it grows, its 
short life cycle, its practically complete self-pollination (i to 10,000 in this 
locality) in outdoor cultures, its comparatively small number of chromo¬ 
somes (seven pairs), the sharp cleavage in its multitudinous character dif¬ 
ferences, and the slight trouble involved in making successful crosses. 
On the other hand, back-crossing for various purposes, such as Morgan 
and his coworkers do, is practically out of the question with peas, because 
of the very small amount (2 to 4) of seed obtained from each cross for 
the amount of work required. 
The material upon which the original and confirmatory data in this 
study are based consists of a collection of over 200 different varieties 
and species of peas gathered from all over the world through the help 
of the Offices of Foreign Seed and Plant Introduction and Forage-Crop 
Investigations; Sutton & Sons, Reading, England; P. Vilmorin and 
Vilmorin et Cie., Paris, France; W. Bateson and C. Pellew; Haage & 
Schmidt, Erfurt, Germdny; several botanic gardens in Europe and Asia; 
and from many other sources. The material particularly used consists of 
the varieties listed in Table I, for which the factors directly concerned in 
this study are also given. All the strains have been inbred for at least 
two generations, and they breed true to the factors designated for them. 
All the pedigree cultures to be compared with one another were grown 
as nearly as practicable under the same environmental conditions—for 
example, the parents and the F x and F 2 generations are often grown side 
by side; crosses are practically all made in the greenhouse in winter; and 
the seed for growing the F 2 progeny are also grown under these conditions, 
as a greater quantity and better quality of seed can be secured than in 
field cultures. Under such conditions the bagging of emasculated flowers 
is absolutely unnecessary. * Under extremely favorable conditions three 
generations a year can be grown, especially by using dwarf short-cycled 
Journal of Agricultural Research, 
Washington, D. C. 
led 
(167) 
Vol. XI, No. 4 
Oct. 22, 1917 
Key No. G—123 
