Abstract
From the meiotic study of Oryza sativa L., the writer concluded that in regard to the genome of the plant, 12 is not the basic number in the strictest sense, but 5 is the primary one from which the 12 had been derived. In other words, Oryza sativa L. is a doubly hexasomic tetraploid plant which may be represented diagrammatically as follows: n=12 A1 A2 B1 B2 C1 C2 C3 D1 D2 D3 E1 E2
Data suggesting the above conclusion are as follows:
(1) In the course of meiosis, the writer observed quadrivalent association at diakinesis and metaphase I in the normal diploids (figs. 3 and 21, s. also Pl. I-6).
(2) Seconday association of the meiotic chromosomes is very distinct; the maximum association has been two groups of three and three groupe of two (fig. 4 out of 4-6 (PMI), 10 & 11 out of 7-20 (MI) and 22 (AI), and 24 out of 23-28 (MII), s. also Pl. I). The results of observation in the three stages of PMI, MI and MII are seen in table 1 and diagram 1. Average numbers of association in the above three stages are 4.83, 3.73 and 4.37 respectively.
(3) Results of many cytological and genetical investigations by various authors have been reviewed, in which the autosyndetic association of the chromosomes has been repeatedly observed in haploid, diploid and triploid plants and the occurrence of duplicate as well as triplicate genetic factors and the phenomenon of genetic “shift” are reported. These all seem to suggest that O. sativa L. is of secondary polyploidal nature.
