and finally a decrease at eighteen rows (Fig. 1). 
The general effect of introgression in reducing row- 
number appears to have a secondary effect in reducing 
the amount of fasciation. This is suggested by the fact 
that fasciation is significantly less frequent in ‘Tripsacoid 
cobs (fourteen percent in grade-4) than in non-Tripsacoid 
ones (seventeen percent in grades-2 and 3). Apparently 
such an effect accentuates a tendency for fasciation to be 
concentrated in the high row-number, non-Tripsacoid 
cobs. 
Diameter. Cob diameters in the Richards’ Caves col- 
lection average 18.3 mm. Teosinte introgression has no 
significant effect on diameter in this population (Table 
III and Fig. 2). 
Length. The length of 433 intact specimens from 
Richards’ Caves averages 8.74 cm. The average in this 
case has little meaning, since, as is shown later, at least 
two factors are interacting to produce the variation in this 
collection. The longest and shortest cobs are the most 
Tripsacoid (Fig. 8 and Plate XXVIII). The fitness of 
the data to a parabolic curve is excellent (Table III). 
Internal Characters. Teosinte introgression appears to 
affect the internal characters of the cobs from Richards’ 
Caves as follows: it decreases pilosity, increases cupule 
width, and increases glume length. Rachis diameter and 
glume-rachis ratio appear not to be closely associated 
with introgression in the samples studied (Table IV). 
Kernels. A majority of the 140 mature kernels from 
Richards’ Caves have a yellow, flinty endosperm; the 
remainder are floury. A few of both types have a red 
pericarp. The dimensions (Table V) show that the grains 
are quite uniform in size and probably are too large to 
pop. Almost half of the grains are definitely immature. 
{ 110 | 
