It is not clear precisely what is represented by the firm- 
ness of the cob but it probably expresses at least two sep- 
arate factors—the strength of the stalk to which the base 
of the caryopsis is attached and the rigidity of the glumes. 
The firmness of the cob is associated also with resistance 
to shattering. Ears of the Andean types usually shatter 
easily while some of the more Tripsacoid varieties and 
segregates from maize-teosinte crosses can be shelled only 
with difficulty. Tripsacum seems to impart to its deriva- 
tives a decided coriaceous quality which affects all parts 
of the cob and, indeed, practically all parts of the plant. 
Size and shape of seeds 
Tripsacum seeds are quite small and it would be ex- 
pected that size of seed in maize would decrease with the 
amount of Tripsacum admixture. This has proved to be 
the case. Three measurements, number of seeds per row, 
number of seeds per unit (one cm.) of row and weight of 
ten seeds, all concerned with the size, and, to some extent, 
with the shape of the seed, show highly significant dif- 
ferences between the low and high groups. The greatest 
difference is shown in weight of seed which suggests that 
shape is a minor factor, as it is not involved in weight. 
There is little doubt, however, though it has not been 
demonstrated statistically, that differences in shape are 
also associated with knob number. We have not suc- 
ceeded in devising any simple method of measuring the 
differences in shape though it is apparent that they exist. 
Among the low-knob group for example, are found ears 
of the Andean type in which the caryopses frequently 
approach a spherical shape and in which there is a con- 
siderable variation in size. These characteristics, com- 
bined with the irregularity in rows and the short tapering 
ear, make the entire structure comparable to a compact 
bunch of grapes. In the high-knob group, on the other 
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