WHITE— STUDIES OF INHERITANCE IN PISUM. 525 



is mature. Y stands for yellow pigment and so far as known is 

 common to all varieties of peas, whether green or yellow seeded. 

 Green when present masks or covers up yellow pigment, hence is 

 epistatic. The factor formulas for all varieties of peas so far genet- 

 ically studied then are : 



YYGGII = true breeding yellow cotyledon races, 



YYggii = Goldkonig (on the present data), 

 YYGGii = true breeding green cotyledon varieties. 



On the basis of these three formulas and by various combina- 

 tions of these three types of varieties, all the various ratios de- 

 scribed in preceding pages, as well as others, may be obtained. All 

 genetic data, so far as I am aware, accord with this interpretation. 



3. Cotyledon Form (Seed Form) and Composition 

 The seeds of peas as regards shape are either smooth round to 

 roundish, or wrinkled and angular. The cotyledons of the seed are 

 mainly responsible for these differences. Smooth, roundish peas, 

 however, are often pitted or dimpled and this dimpling is of two 

 types. One type is largely due to such environmental conditions as 

 premature harvesting, while the other type remains pitted under 

 practically all common environmental conditions. The latter type 

 is designated " slightly wrinkled " by Tschermak and " indent " by 

 the English geneticists. Indent, while a character which modifies 

 the external appearance of the seed and cotyledon, belongs in reality 

 to the generation preceding that to which the cotyledon characters — 

 wrinkledness, color, etc., belong. Associated in inheritance with 

 seed form are certain types of starch and certain germination, sugar 

 content and color modifying characters, and because of this asso- 

 ciation they will all be considered under this heading. Indent peas 

 and smooth peas will be treated separately. 



Smooth round peas without indenting are most commonly char- 

 acteristic of varieties with white flowers and colorless seed coats, 

 although many varieties with colored flowers and colored seed coats 

 have perfectly smooth seeds. Particularly is this true of most of 

 the wild sorts, all of which have colored flowers. The starch grains 

 of the smooth-seeded varieties according to Gregory (^y), Darbi- 



