Oct. 22 , 1917 
Inheritance Studies in Pisum 
171 
Factors A, C, E, (Gc), and L 1? so far as the evidence forthcoming up to 
now is concerned, appear absolutely coupled, and it is much simpler to 
regard them all as one factor with many separate expressions. A 
could be substituted in each case where C, E, (Gc), and E t are used. 
MODIFICATION OF THE EXPRESSION OF PISUM FACTORS BY DIFFER¬ 
ENT ENVIRONMENTS AND BY EACH OTHER 
Most of these data have been compiled from other papers, but this 
brief review also represents for the most part, first-hand confirmatory 
knowledge by the writer. References to literature and credit are given 
in the earlier paper previously referred to. 1 
The factor expressions given in Table II represent only the usual or 
common expression, and changes in environment may quite radically 
modify these expressions. Weather conditions, especially prolonged 
damp or rainy weather, often wash out or suppress the development of 
the purple flower color, so that, it resembles the pink, and pinks are 
modified by the same causes to white. Under greenhouse conditions, 
where proper control is exercised, this never happens. Factors 3 and 
35, either independently of each other or when combined, produce the 
glaucous waxy covering of peas. Factor 3 is arbitrarily regarded as the 
common one. Plants from which either or both of these are absent are 
called “emeralds,” and lack this covering. Such plants are very sub¬ 
ject to death from disease and other external causes; hence, are gener¬ 
ally deficient in number in the F 2 ratios from crosses of glaucous with 
emerald varieties. The usual expression of factor (Bt) (4) depends 
partly on whether the pod is well filled with peas. Factors C and D (5, 6) 
are dependent on plenty of sunlight; otherwise the color is either com¬ 
pletely absent or faint. The anthocyanin pigment of the seedcoat pat¬ 
tern, brought about by the presence of factors E and F (7, 9) is soluble in 
water and may be washed out in rainy weather. Factors (Ef) and (Ef) 
(8, 21) are modified by a large number of environmental conditions, so 
that studies on these should always be carried on with parents, F t , F 2 s, 
etc., growing side by side from plantings made at the same time. In 
crosses between certain normal and fasciated varieties of peas, domi¬ 
nance may be partially reversed by cloudy weather and conditions very 
favorable for rank growth. Unfasciated stem is usually dominant over 
fasciated stem, but in such crosses as noted above, the F t plants have 
been slightly fasciated under the conditions mentioned, while under other 
conditions, Fj plants of the same cross have remained normal. 
A character similar to that produced by the absence of factor (Fa) 
(10) may be brought about in varieties of peas in which (Fa) is present 
by very damp weather, lack of sufficient sunlight, and crowding and 
twisting of the stems (White, 1916b). Various environmental causes 
7768°—17 -6 
1 Whits. O. E. Op. cit. 
