\ 
gression. (1)) The apparent relationship of chromosome- 
knob numbers with geographical distribution is a fallacy 
or is not pertinent to the problem. (E) The chromosomal 
characters of corn, teosinte, and T'ripsacum are not con- 
sistent with the theory that teosinte originated as a hybrid 
between corn and Tripsacum. (IF) There is no cytological 
mechanism by which the terminal knobs of Tripsacum 
could have assumed the internal positions now found in 
some varieties of teosinte. (G) The fact that teosinte is 
intermediate between corn and 'Tripsacum in plant char- 
acters is of minor importance. 
These objections will be considered in the order named, 
with emphasis on recent results obtained by various in- 
vestigators; for completeness two additional topics will 
be discussed. 
Possipitity or NatTuRAL HYBRIDIZATION OF 
Corn AND 'T'RIPSACUM 
The first crosses of corn by Tripsacum, on which our 
earlier studies were based, were made only after remov- 
ing the shucks of corn and pruning the silks. But we 
have found since 1939, as Randolph also has, that the 
pruning of the silks, although probably helpful, is not 
essential to hybridization. 
Since they appear to have been overlooked, we shall 
repeat two possibilities previously mentioned (26) by 
which corn might become hybridized naturally with Trip- 
sacum: (a) the occurrence of ears which protrude beyond 
the shucks, a common character in certain varieties; (b) 
silks exposed to the base through mutilation of the 
shucks by insects or by holes bored by larvae. 
Weatherwax’s own publications (51, 52, 53) mention 
or describe at least four additional conditions in corn— 
depauperate plants with terminal pistillate inflorescences, 
homozygous pod corn, flowering tillers and his hypo- 
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