遺伝学雑誌

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In the previous paper, one of the writers (Matsuura) gave three different chromosome counts, n=21, 35 and 42, in three different plant groups of Phacellanthus tubiflorus, a parasitic herb. That this species is highly polymorphic from the karyological view was further ascertained in the present paper by the discovery of several other karyotypes, 19_II (Fig. B. 2), 38_II, (Fig. B. 3), 19_III (Fig. D) (which is presumed as formed by the natural hybridization between the former two types), 38_II+1_I (Fig. B. 5) and 39_II (Fig. B. 4). The material was obtained from roots of several different plant species, such as Ulmus lacinata, Cornus controversa, Morus bombycis, Kalopanax ricinifolium var. typicum and _{Picrasma quassioides}.
The characteristic features of the meiotic metaphase of these types are (i) that no multivalents are formed, (ii) that the secondary association of bivalents occurs in a marked fashion (Fig. E) and (iii) that non-disjunction and non-conjugation (Fig. D. 9, B. 2) of certain bivalents are frequently met with. The last feature is considered as related with the formation of the aneuploid forms.
The meiotic metaphase of the 19_III type is characterized by the occurrence of bivalents and univalents, no trivalents being formed, the combinations of them ranging from 19_II+19_I to 26_II+5_I (Table II), thus indicating the possibility of autosyndesis in the members of the haploid set. This suggests together with evidences from the secondary association of bivalents and also from the morphological comparison of the chromosomes in the haploid set (Fig. C. 6) that the basic number 7 which was inferred from the numerical consideration on the 21-35-42 series is also applicable to the present 19-38 series.
The comparison of morphological characters in these several karyotypes reveals only differences with minor importance, which may be ascribed to the limited habit of living of this plant, i. e. parasitism.

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At the meiotic prophase of the PMCs in Rhoeo discolor Hance, twelve chromosomes conjugate end-to-end forming a ring, a chain or several chains, a condition which was attributed by Sax (1931) and others to the segmental interchange between non-homologous chromosomes. Non-disjunction of meiotic chromosomes has been observed by several authors to occur with tolerable frequencies. The present author has studied non-disjunction of meiotic chromosomes in connection with the pollen fertility. The observation on 100 metaphase plates which were obtained from acetocarmine preparations showed the following facts.
1) Non-disjunction of adjacent chromosomes in a ring or a chain occurs in about one-third of the pollen mother cells observed (Table 1).
2) The occurrence of such non-disjunction is restricted to relatively long chains (Table 2).
3) Non-disjunction of adjacent kinetochores connected by two short arms occurs more than seven times as frequently as those by long arms (Table 3 and Text-figs. 1-4).
4) Another case of non-disjunction takes place in cases of more than two chains, suggesting that each chain constitutes a system independent of one another regarding chromosome movement (Text-figs. 4-6).
5) Pollen grains which received at least one complete genome are capable of the further nuclear divisions, but those containing less than one genome degenerate soon after the tetrad formation (Text-figs. 7 and 8).
The expectation for the pollen fertility calculated from the present data (Table 4) is approximately close to the actual pollen fertility examined in acetocarmine preparations (Table 5).
Disjunction and non-disjunction of adjacent kinetochores in a ring or a chain must depend upon the behavior of polar granules at diakinesis and metaphase. The investigation on these matters is now in progress.

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