34 Journal of Agricultural Research voi. n. No. i 
upon the structure of the cells in the various tissues, it was found that 
they were not so useful for an examination of the pigments and their 
distribution as sections made transverse to the seed coat or, in other 
i 
words, perpendicular to the surface of the cowpea. 
A large number of reagents were experimented with, but eventually 
it was found that those of practical use were extremely few—namely, 
distilled water, alcohol, ether, chloroform, xylol, solutions of caustic 
soda and caustic potash (the i per cent solutions being of greatest 
service), dilute hydrochloric acid, normal Fehling’s solution, saturated 
aqueous solution of chloral hydrate, peroxid of hydrogen solution, and 
several stains, the most satisfactory being a 50 per cent alcohol solution 
of diamond fuchsin and a 10 per cent aqueous solution of pyronin. As 
above stated, these were used upon sections mounted dry under the cover 
glass, the various liquids being drawn through by means of triangular 
pieces of blotting paper placed at the opposite side of the cover glass. 
The length of treatment varied under different circumstances from a 
few seconds to 24 hours. However, most of the reactions that were 
significant were obtained within a few minutes, so that study could be 
rapidly carried on. 
As the problems in mind had to do with the differences in the color 
schemes of cowpeas as a whole, only a general examination was made to 
learn in what respect different areas of the seed coat were differently 
pigmented. It became evident that although the pigment intensifica¬ 
tion varied in different areas of the seed coat, a general idea of the color 
scheme could best be found by studying sections taken from the side of 
the seed. The greater intensity of color around the hilum was found to 
be merely due to a larger quantity of the same pigments as those present 
on the side of the seed, and very frequently this heavier pigmentation 
proved to be a disadvantage, as, in the case of dark colors, they fre¬ 
quently obscured less intense pigments easily detected in sections made 
where coloration was not so dense. The only case where the pigmenta¬ 
tion near the hilum was particularly worth studying was in those varieties 
where colors on the general surface were lacking—namely, in the cream- 
white and pure-white varieties. In this class the varieties that have 
a more or less intense pigmentation around the hilum give some informa¬ 
tion as to the tendency of general pigmentation that such a variety might 
be expected to show were the whole of the seed coat colored in the usual 
way. 
MORPHOLOGY OF THE SEED COAT 
Before discussing the coloration schemes in different varieties of the 
cowpea it is necessary to describe the structure of the seed coat, espe¬ 
cially as seen in transverse sections. Such sections show that it may be 
divided into three layers. The outer layer is a single row of elongated 
palisade cells, with their long axis perpendicular to the surface of the seed 
