the artifacts are like those of San Lorenzo, but new 
point and pottery types occur as do large choppers and 
scrapers. Historic goods were present in some levels, and 
the woven twilled mats, coiled nets and cloth were much 
simpler. 
Though the culture phases mentioned above seem to 
represent a unilinear development, the area, situated on 
the northern peripheries of Meso-America, must have 
had many influences at different periods from the south. 
It is believed that this peripheral region reflects, perhaps 
with some time-lag, the general sequence of agricultural 
practices for all of Middle America. Its geographical 
position just north of Meso-America indicates that it is 
a key area for the understanding of diffusion of agricul- 
ture into North America. 
The study of our bean remains from the Tamaulipas 
caves, which seems to bear out these generalizations, also 
has considerable bearing on the solution of the problem 
of the origin and dispersal of prehistoric beans in the 
New World. 
IDENTIFICATION OF MATERIALS 
The materials examined consist primarily of desiccated 
and uncharred bean pods and fragments of pods. Seed 
remains are few and often fragmentary. Since most of 
the materials mentioned in this paper are pods, a brief 
discussion of the nature of legumes will be helpful. 
In the Leguminosae, gross morphology of the fruit 
may be diagnostic in species-determination and is useful 
in delineating varieties of polymorphic species such as 
Phaseolus vulgaris. 'The legume or pod is a single carpel 
with two identical valves dehiscing on dorsal and ventral 
sutures. At the basal end, these elongate valves diverge 
from a pedicel and terminate at the apex in a straight or 
curved tip. Behavior of the pods at dehiscence is related 
[ 39 | 
