to their anatomy and may differ markedly in different 
varieties. When the fruit is mature and dry, the valves 
split along dorsal and ventral sutures after which they 
may simply separate or they may twist to varying de- 
grees. Twisting results in dislodgment of seeds and proba- 
bly aids in their dissemination. The twist of one valve 
is the mirror image of the other, and the twist of both 
is the result of a shortening of certain fiber-cells in the 
pod-wall. 
In the production of beans which are threshed after 
the pods and seeds mature and dry on the plants, it is 
essential that the pods be of the type which do not de- 
hisce violently with the consequent scattering of the seeds 
prior to threshing. The manner of dehiscence is of little 
importance in varieties which are customarily harvested 
during damp weather or which are used in the green stage. 
Explosive scattering of seeds probably occurs in all wild 
species of the genus Phaseolus and the loss of this char- 
acteristic must have been one of the important features 
of domestication and variation in beans. 
The pods, and other vegetal debris examined, had been 
placed in separate packets, according to the site of collec- 
tion, culture and occupation level. When the relative 
quantities of materials present in each occupation level 
had been estimated, tentative species-identifications were 
made. Many of the twisted and folded pods were ex- 
tended and pressed after softening in warm water with 
a detergent to facilitate their identification. 
Phaseolus vulgaris (common beans) and P. lunatus 
(the small seeded or sieva group of lima beans) were rec- 
ognized on the basis of their gross morphology. P. coc- 
cineus (runner beans) pod fragments were at first classified 
only as leguminous remains, probably of a species of 
Phaseolus or a closely related genus. These remains of 
P. coccineus were later identified on the basis of the hilum 
[ 40 ] 
