M. OKAMOTO
Department of Genetics, University of Missouri, Columbia, Mo., U.S.A.
On the basis of the fact that the model number of bivalents in the F1 of Beta-speltoid x T. boeoticum Boiss. (T. aegilopoides Bal.) was the same as that observed by Hosono (1935) in the F1 of T.persicum rubiginosum (21II) x T. boeoticum Boiss., Matsumura (1951) concluded that the chromosome missing in the Beta speltoid was in the B genome1).
In four different 27-chromosome F1 plants of the cross mono-IX Chinese and T. boeoticum Boiss., chromosome pairing was as follows: (3 and 4 were calculated as 1II + 1I and 2II, respectively)
The data suggest that:
(1) The model number of bivalents tends to be the same or not very widely different in samples taken on the same day from the same plant or even from different plants.
(2) The mode varies according to the day on which the sample is taken.