A COMPARATIVE STUDY OF THE KARYOTYPES OF VERNICIA FORDII AND V. MONTANA

Vernicia fordii(Hemsl.)Airy-Shaw(Aleurites fordii Hemsl.)and V. montana Lour.(A. montana(Lour.)Wils.)(Euphorbiaceae)are two Chinese important tung oil trees widely cultivated in the regions south of the Yangtse River. They are very similar to each other both in morphology and in anatomy. A comparative analysis of the karyotypes were carried out in order to shed some light on the phylogenetical relationship between the species in question. The number of chromosomes in growing tip cells of shoots of both species is found to be 22, consistent with the reports of Mehra, Bedi and al. and other authors. According to the terminology defined by Levan and al., the karyotype formulae are both 2n=22=22m. In the light of Stebbins' classification of karyotypic asymmetry, both karyotypes belong to "1A" type and should therefore be considered as very primitive ones. But there are a few minor yet notable differences between the two karyotypes:(1)the constant occurrence of a secondary constriction on each of the long arms of the 5th pair of chromosomes in V. fordii, but absent from V. montana;(2)the differential value of relative length of chromsome set of V. fordii(5.38)being 1.4 times as much as V. montana(4.71); and(3)the differential value of arm ratio of V. fordii(0.53)being 1.94 times as much as V. montana(0.18). These data show that the karyotype of V. fordii is to some extent less symmetrical than V. montana, and should therefore be considered as phylogenetically more advanced than the latter. Since plants of V. fordii have hitherto never been found in natural conditions, it is suggested that the species may probably be a derivative of V. montana over a long historical period of artificial selection and cultivation by ancient Chinese people.