Normal plants of Lillium Hansonii (2n=24) form always 12_II at IM (in 200 metaphasic plates observed) (Fig. 1). A plant heterozygous for a reciprocal translocation showed invariably 1_IV+10_II at that stage (in 342 cases observed) (Fig. 2). The metaphasic configuration of the tetravalent was a ring modified by a number of interstitial chiasmata. This type of metaphasic configuration is a conclusive evidence that the translocation is reciprocal.
It is an important point revealed by the present study that in this plant the kinetochores of the homologous chromosomes retained paired until the IA in bivalents as well as in tetravalents (Figs. 1-2).
In tetravalents the chromosome part between the paired kinetochore and the chiasma nearest to it frequently appears very short (Figures of such cases not shown). Considering the above fact interchanged chromosomes Ab and Ba are obviously the result of a mutual trans-location of the major part of both long arms of the normal chromosomes Aa and Bb (cf. IIA in Fig. 3).
2.1 (in 240 cases observed) and 2.2 per cent. (in 831 cases observed) of PMC_s at IA was irregular in normal and reciprocal translocation plants respectively. A majority of irregularities are bridges not accompanied by fragments and their configurations indicate that they result from a half-twist between the chromatids of a dyad (Fig. 4, a-i). The others are bridges accompanied by fragments which would have probably originated from chromatid fragmentation and fusion (Fig. 4, j-k).

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