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A cytological analysis was made with root-tip meristematic cells of regenerated plants and their offspring originated from tissue cultures of Nicotiana tabacum cv. Wisconsin No. 38. Each original regenerate showed a wide range of variation in chromosome number, irrespective of combinations or concentrations of growth regulators used for regeneration. Two regenerates designated Nos. 1 and 2 were used for the analysis of further generations. In the first selfed generation (S1), all the progenies of both Nos. 1 and 2 exhibited variable chromosome numbers. Five plants derived from No. 1 had 43.0±1.0 chromosomes on the average, while two plants from No. 2, 63.7±1.9. The majority of S1 plants of No. 1 showed normal or hypoploid chromosome numbers, whereas hyperploid numbers were common in S1 plants of No. 2. In the second selfed generation (S2), the chromosome number of all the progeny plants of No. 1 stabilized to 48, whereas all the S2 plants of No. 2 exhibited still highly variable chromosome numbers. Moreover, all the plants belonging to the No. 1 lineage were almost normal physiologically (pollen and seed fertilies, plant height, leaf color, leaf from, inflorescence shape and etc.). In the No. 2 lineage, in contrast, these characteristics segregated frequently, and most of the plants exhibited, more or less, some anomalies. Observations of mitotic anaphase revealed that there exist considerable irregularities such as anaphase bridges. These results indicate that the lineage of No. 2 possesses some genetical and/or physiological factor(s) leading to the cytological instability. From the reciprocal crosses between No. 1 and normal plants, existence of a cytoplasmic effect on the cytological stabilization was also presumed. To determine the existence of the gene(s) involved in the present cytological chimerism, further studies on the crosses involving the No. 1 lineage are required.

THE CYTOLOGICAL CHIMERAS IN ORIGINAL REGENERATES FROM TOBACCO TISSUE CULTURES AND IN THEIR OFFSPRINGS