MULTIPLE FACTORS 225 
the next generation when the plant of that composi- 
tion is self-fertilized. It will be observed that the 
1:0 ratio is expected 7 times. 
3:1 ratio is expected 4 times. 
15:1 ratio is expected 4 times. 
0:1 ratio is expected 1 time. 
This test was applied by Shull to his F, plants of the 
triangular type. There were seven families that 
gavea 1:Oratio, four that gave approximately a 3:1 
ratio, and six that gave a 15:1 ratio. These results 
are in fair accord with the expected numbers given 
above. 
When a further test was carried out by breeding 
from the six 15:1 families of the F; group above 
(which should be expected to give the same results 
as the F, class, because they have the same composi- 
tion), the ratios obtained were as follows: 
1:0 ratio expected 35; realized 39. 
3:1 ratio expected 20; realized 12. 
15:1 ratio expected 20; realized 26. 
The results agree again fairly well with the expecta- 
tion. 
A second test is found in self-fertilizing plants from 
families that gavea 3:1 ratio. As the diagram shows 
these contain only the one (‘‘c’’) or the other (‘‘d’’) 
factor, they should give only homogeneous families 
and 3:1 families—never 15:1 families. This result 
also was obtained. 
Nilsson-Ehle found that three recessive factors 
must combine to produce an effect which, in the 
