attention, and Weatherwax (51) accepts it as a fact. 
Randolph (81, 32) does point out that 7. maizar and 7. 
australe are knobless or nearly so, and since he assumes 
that these are the only diploid Tripsacums native to Mex- 
ico and Guatemala, he concludes that any species of 
Tripsacum which might have hybridized with corn to 
produce teosinte must have been a knobless form. But 
it has already been explained that there are reasons for 
the opinion that 7' dactyloides, or possibly one of its 
parents, was present in or near Guatemala in prehistoric 
times. 
An objection has been raised (81) that the hybrid origin 
of teosinte requires its chromosomes to be intermediate 
between those of its putative parents in length and num- 
ber. This objection is not valid. What should be expected 
does occur: the chromosomes of teosinte are similar in 
length and number to those of its hypothetical recurrent 
parent, corn. It is also important to note that Maguire’s 
(21, 22) reports of exchanges between corn and ‘Tripsa- 
cum chromosomes do not indicate that length and num- 
ber of chromosomes were affected. 
Objections to the hypothesis of the hybrid origin of 
teosinte have been made (31, 82) on the additional 
grounds that the chromosomes of teosinte are “‘so simi- 
lar to those of corn and so dissimilar to those of Trip- 
sacum that it seems highly improbable an exchange of 
segments could have occurred on a sufficiently extensive 
scale to account for the hybrid origin of teosinte.. .”’ 
The discussion immediately preceding the section which 
is here quoted shows that the writer was referring to sim- 
ilarities and dissimilarities in length and arm ratio. But 
there is no known reason why such differences should 
prevent the exchange of segments. It is well known, for 
example, that in heterozygous translocation stocks of 
corn, chromosomes differing widely in length and arm 
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