claimed to be, has come to have different numbers of 
knob positions without extensive chromosomal rearrange- 
ments, perhaps a fraction of the problem of the origin of 
corn would be solved. But there is as yet no explanation. 
Longley (19, 20) interpreted his data as supporting the 
hypothesis of a series of inherited gradients. However, 
this hypothesis has been discredited by Mangelsdorf and 
Cameron (23) and by Rhoades (41) in several ways. 
Rhoades points out, for example, that the interpretation 
is without experimental evidence and is contradictory to 
the often observed fact that when a knob is shifted by 
rearrangement from one position to another its appear- 
ance does not change. Randolph (82) contributes a single 
sentence which constitutes his most positive explanation : 
The present status of the problem concerning differences with respect 
to the prevalence of terminal and intercalary chromosome knobs in 
corn, teosinte and Tripsacum forces one to the conclusion that gene 
mutation rather than hybridization accompanied by structural chromo- 
somal alterations has produced these fundamental differences in chro- 
mosome morphology. 
He then states that his conclusion is similar to that of 
Longley (19) but does not sufficiently expand his idea to 
make it clear and convincing. So far as his explanation 
goes, it is very well in agreement with the theory that 
teosinte is a hybrid; it simply means that teosinte is in- 
termediate between corn and ‘Tripsacum for genes con- 
trolling number and position of chromosome knobs. But 
Randolph’s explanation seems to meet with the same 
difficulties that Rhoades pointed out with respect to 
Longley’s. 
Randolph’s (82) favorable attitude towards the view 
that modern corn is a composite of several wild species 
of Zea might have been intended as a possible explana- 
tion of the various knob numbers and positions now 
known. But even so, it contributes nothing towards a 
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