40 Journal of Agricultural Research voi. n. no. i 
red or dull reddish brown, uniformly spread over the seed coat. If the 
palisade layer contains uniformly anthocyanin in its cells, the basal color 
is obscured or modified by this superimposed pigment and assumes a 
blue or black or purple tint. If the palisade cells are irregularly pigmented, 
all of the modifications in marbling, speckling, and streaking which serve 
to distinguish the different varieties of cultivated cowpeas are found 
(PI. VI, fig. 2). It may therefore be said in general that the diversification 
in color is principally brought about by the deposit in the palisade cells 
alone of the pigments above mentioned and that the different tints of 
color tones are the result of the various combinations of pigment already 
mentioned. 
SEEDS DESTITUTE OF PIGMENTATION 
Some reference should be made to such cowpeas as are more or less des¬ 
titute of pigmentation. The writer examined only one cowpea the 
entire seed coat of which gives no evidence of pigment deposit; but among 
the large number of white and cream-white cowpeas there are probably 
several others quite destitute of pigmentation—that is, true albinos. In 
fact, four other varieties of white or cream-white cowpeas were examined 
in which the maximum quantity of pigment was so minute as to make its 
detection quite difficult, and certain individuals of these varieties, after 
the most painstaking tests, left the question in doubt as to whether or not 
even a trace of pigment was present. They were Nos. 212-2-11,212-6-8, 
213-2-4, 2i4~3-2Re. From the standpoint of coloration, therefore, 
these pure white and cream-white varieties may all be safely considered 
as albinos. The strict albino examined was No. 0632. Most careful test¬ 
ing failed to disclose any coloration in the palisade layer or in the basal- 
color layer, long treatment with various reagents resulting merely in such 
faint tints as would be secured by reactions on the normal cell contents, 
such as cytoplasm and nuclear substances. With the exception of these 
albinos, all the cowpeas examined have more or less pigment deposited 
in the basal-color layer, and, as before stated, this is of a melanin-like 
character. When the palisade layer is destitute of pigment, uniform tinted 
cowpeas are obtained, ranging from a cream-white seed coat, where the 
amount of pigment in the basal-color layer is very small, to a strong buff 
or even red brown, where the amount is greater. 
After this general consideration of the structure of the seed coat and 
of the various ways in which its color layers are pigmented, the chief 
varieties of cultivated cowpeas may be described individually. The varie¬ 
ties here enumerated represent in a general way all the known color 
schemes found in cowpeas. They were chosen at the suggestion of Prof. 
W. J. Spillman, of the Bureau of Plant Industry, who proposed this line of 
investigation, these types being those used by him in connection with 
certain studies in hybridization. 
