28 
places us more and more in a position to combine many charac- 
ters together in a very definite fashion. In mapping the heredi- 
tary make-up of peas, we have been combining the characters ot 
various varieties into one variety, so as to make it unnecessary to 
deal with so many kinds. We now have varieties that differ from 
each other in as many as thirteen clear-cut characters, the tn- 
heritance of each of which is comparatively simple. Of course, 
they differ in many more characters, but these others are com- 
plex in their hereditary make-up; just as in the inheritance of 
pod size, of yield, and of time of flowering, many hereditary de- 
terminers, as well as many environmental conditions, govern the 
coming into being of the last mentioned type of characters. For 
this reason, for some problems, they are not so desirable to work 
with. Some characters are very sensitive to apparently slight 
differences in environment; others are not. For example, flower- 
color, various seed-coat colors, flowers in bouquets or umbels at 
the top of the plant or distributed along the stems as in ordinary 
peas, seeds stuck together in the pod (chenilles) or free as in 
ordinary varieties, scimitar-shaped pods, or straight pods, and 
many others are comparatively insensible to ordinary changes in 
—y 
environment. 
During 1926, studies on the inheritance of a new striping pat- 
tern of the seed-coat have, for the most part, been completed. 
This pattern, in the original form in which we obtained it, con- 
sisted of broad purplish stripes on a reddish gray seed-coat. The 
seed came from A. D. Darbishire (in England), who secured it 
from crossing a Chinese native pea with a form of “ Pisum wim- 
bellatum,’ a pink-flowered fasciated pea. He sent it to us as a 
true-breeding segregate for certain characters. So far as we 
know he never described it. We later obtained the same pattern 
from crossing a white-flowered Chinese pea that we obtained in 
Chinatown, New York City, with several colored-flowered va- 
rieties that we had produced ourselves. The Darbishire variety 
in our cultures is known as P 5, the white-flowered Chinese type 
from’ Chinatown is P 50. P 5, when crossed with a variety 
having pink flowers and non-striped seeds, gives all striped 
seed plants in the first hybrid or F, generation and a ratio ap- 
proximately of 3 plants with striped seeds to one without in the 
