The reappearance of Phaseolus coccineus after the be- 
ginning of Palmillas suggests strongly the response of 
a wild rather than cultivated plant. We would hardly 
expect a cultigen absent for 2000 years to be reestablished 
merely with the return of favorable climatic conditions. 
Reintroduction is a possibility, but from where? The 
southwestern United States could not have been a source 
for reasons already noted. Plant migration from regions 
south of Tamaulipas would have been highly unlikely, 
since conditions there would have been even less favor- 
able for the survival of a cultivated plant with cool tem- 
perature requirements. An indigenous plant, on the 
other hand, might have formed relic communities in pro- 
tected locations becoming more generally distributed and 
available for human use at the end of the thermal period. 
A second thermal period might well have been the cause 
of the extinction of P. coccineus from this part of its nat- 
ural range. 
The hypothesis that Phaseolus coccineus may have been 
a wild rather than a cultivated plant in ‘Tamaulipas is sup- 
ported by the extreme age of the remains and their occur- 
rence long before the practices of ceramic cooking and 
agriculture, and by the apparent lack of selection for pod 
characteristics found in modern cultivated varieties. If 
runner beans were present, but not domesticated, in 
Tamaulipas in spite of their being included in the gath- 
ered plant complex prior to and during agricultural 
times, another problem arises. Why would so useful a 
food plant be neglected as a domesticate in Tamaulipas 
but be brought into cultivation in Chiapas? The answer 
is to be found probably in the reaction of P. coccineus to 
the differing photoperiods in these widely separated areas 
of its range. 
Allard and Zaumeyer (1944) studied the reaction of 
various leguminous plants to day-length. A daily expo- 
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