NEO-MENDELISM IN PLANTS 421 
but we shall not attempt to list all of the proposed types. A simple 
illustration of the better known types is as follows: 
a) A complementary factor is added to a dissimilar factor to pro- 
duce a particular character. , 
b) An inhibitory factor prevents the action of some other factor. 
c) A supplementary factor is added to a dissimilar factor with the 
result that the character is modified in some way. 
d) A cumulative factor, when added to another similar factor, 
affects the degree of development of the character. 
Some examples of these types will make them clear, those for 
complementary factors having been given previously. 
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Pure Red Parent Gamete White Parent with 
Red Inhibitor 
Fi White 
Fic. 80.—Diagram illustrating behavior of inhibitory factor. (From Coulter 
and Coulter.) 
2. Inhibitory factors.—Recalling East’s experiment with red- 
grained corn it will be remembered that when both factors for red 
were present the grain was red, but when either factor was absent the 
grain was white. Later he crossed these strains with a new white 
strain, and the result was surprising. The pure red strain produced 
gametes carrying both the red factors, and it would be expected that 
whatever such a gamete mated with would result in red progeny; but 
when this pure red was crossed with the new strain of white the pro- 
geny were all white, although the hybrids certainly contained both 
factors for red. The explanation which first occurred to East, and 
which later experiments confirmed, was that the new white strain con- 
tained an inhibitory factor, which prevented the development of red 
even though both the complementary factors for red were present. 
