If the experiments by Ghobrial reported above prove to be a method of obtaining homozygotes for parental combinations in multiple interchange heterozygotes, there are several interesting applications. One is the following.

Test crosses have been made to establish a homozygous T6-3-2-4-8-10 stock, i.e., one with T8-10 added to the T6-3-2-4-8 that was used in the above experiment reported by Ghobrial. Since this T8-10 interchange is common to the 5-7-1-9-10-8 stock, F1's from the cross between the two will have two rings of 10. In these plants, barring crossing over, there are only three viable micro- and megaspore 1n combinations: one with one parental chromosome set, one with the other parental set, and the third one with all the interchange chromosomes, i.e., 5-7-1-9-10-8-4-2-3-6. This latter combination occurs without crossing over. The use of F1's from T5-7-1-9-10-8 x T6-3-2-4-8-10 for colchicine treatment should be worth a try.

A homozygote for all those interchanges might be used for gamete selection, but only if crossing over at meiosis is bypassed also.

Chas. R. Burnham

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