COLORATION OF THE SEED COAT OF COWPEAS 
By Albert Mann, 
Plant Morphologist, Agricultural Technology and Cotton Standardization and Grading 
Investigations , Bureau of Plant Industry 
INTRODUCTION 
The following study of the seed coat of various cultivated cowpeas 
(Vigna sinensis) was made because the great diversity in color schemes 
and kinds of pigment in these seeds seems to have a direct bearing 
on problems of heredity, the pigmentation being to a large extent a 
basis for distinguishing one variety from another. It therefore seemed 
desirable that a clear understanding of the morphology of the seed 
coat and the way in which these pigments are arranged in its various 
layers should be obtained, in order to discover whether there are any 
facts bearing on problems of heredity, outside of the mere facts of the 
different color arrangements themselves. It also seemed not unlikely that 
such a study might prove that colors optically alike are in some cases 
different as to the material of the pigment and the place of its deposit. 
METHODS OE PREPARATION 
The best methods for the study of the cowpea pigmentation were 
found to be as follows : 
The seed coats were removed from dry cowpeas in flakes as large as 
possible and were then cut transversely in pith, the sections made by 
hand being as thin as possible. It was found that to embed the seed 
coats for microtome sectioning necessitated subjecting them to water if 
the freezing process was used or to various solvents if celloidin or paraffin 
was used. Both methods resulted in dissolving the pigments to some 
extent and thereby causing them to appear in parts of the seed coat 
where they did not normally belong. The dry method of cutting avoided 
this difficulty. The sections were mounted dry under -inch square 
cover glasses, held in place by a drop of paraffin on either side of the 
glass. By this method the sections may be examined in the dry state 
and closely watched when water, various reagents, or stains are being 
applied, so that facts as to solubility, chemical reaction, etc., may be 
accurately noted. Such sections, held down by an immovable cover 
glass, are also ideal for high-power examination. If necessary, they may 
be also readily preserved for future study. Sections tangential to the 
surface of the seed coat were also made, but, aside from throwing light 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
(33) 
Vol. II, No. 1 
Apr. is, 1914 
G—16 
