hand, the extreme type is one in which the grains are 
flat, uniform in size and shape and very regularly spaced 
in straight rows. 
Endosperm type 
It was suggested by Mangelsdorf and Reeves (18) that 
the pointed-seeded pop corns of Mexico and Central 
America are the most Tripsacoid types which have re- 
sulted from admixture with Tripsacum and that dent 
types originated from hybridization of these with uncon- 
taminated flour corn. ‘The Guatemalan varieties do not 
support this suggestion. Among the high-knob group, 
especially among varieties with ten knobs or more, dent 
corn is the predominating type. No pointed pop corns 
were included in McBryde’s collection, although varieties 
with decidedly pointed seed occur. It is possible that the 
pointed-seed pop varieties are still to be collected in Gua- 
temala but it is also possible that the original assumption 
that they are the most Tripsacoid types is in error. It is 
obvious now that such an assumption is not required inas- 
much as Tripsacum and teosinte are themselves popping 
cereals (Beadle (4); Mangelsdorf and Reeves, unpub- 
lished), and there is no reason why a hybrid of teosinte 
and flour corn should not give rise directly to dent types. 
Such hybrids are now being investigated. 
In the meantime it is clear that there is a relationship 
(P is less than .01) between knob number and dent types 
as opposed to typical flint or flour types. The two latter 
types are combined for purposes of computation. They 
differ from each other primarily by a single gene and there 
are several examples in our collection, of ears almost iden- 
tical in all characteristics except that one is flinty, the 
other floury. Denting, on the other hand, is governed 
by a number of genes and is a complex departure from 
the basic flint and flour types. 
[ 230 | 
