able, it neither stimulates new research nor points to 
possible new methods of maize improvement. In this 
respect, the theory is less useful than the tripartite theory 
which has furnished the impetus for an extensive series 
of researches on maize and its relatives and has also sug- 
gested new possibilities for improving maize. If two 
theories appear to be equal in validity, the one which is 
testable and which stimulates new research is the more 
useful; a theory which is plausible but untestable tends 
to stifle research. 
In emphasizing the differences between the tripartite 
theory and that of common ancestry it should not be 
overlooked that there are also important resemblances 
between them. The two theories agree that (a) corn is 
an American plant; (b) it is descended, with Tripsacum, 
from a remote common ancestor; (c) its immediate an- 
cestor was a freely-branching plant bearing small ears 
with grains enclosed in glumes; (d) corn attained its 
present form through changes occurring during domes- 
tication, which began not more than a few thousand 
years ago. Ina broad sense, then, the two theories agree 
with respect to the place, time and manner of origin. In 
the same broad sense, the problem of the origin of corn 
can almost be said to be solved. 
[ 437 ] 
