Chromosome numbers in Menispermaceæ

Abstract

In a recent communication to nature, entitled, Origin of the Angiosperms, Dr. Anderson puts forward the interesting suggestion of the possible origin of modern flowering plants through the Magnoliales from wide crosses between different groups of Gymnosperms showing 12 and 7 as the base number of their chromosomes, such as the modern Ginkgoales, Cycadales and Coniferales show on one hand, and the Gnetales on the other. The various genera of the Magnoliales show 19 as the base number of their chromosomes, which is rather unusual among other families of flowering plants. We have in this laboratory been working for a considerable time on the cytology of the family Menispermaceaeæ (results not yet published), a close ally of the Magnoliaceaeæ, and have found the haploid number of chromosomes in Tinospora cordifolia, Miers, to be 12, and in Cocculus villosus, DC., 19 (12 + 7). Dr. Lindsay, in Menispermum canadense, Linn., has found the haploid number of chromosomes to be 26 = 19 + 7 = 12 + 7 + 7. It may be asked whether there is any significance in these chromosome numbers in relation to Dr. Anderson's hypothesis. The difference of seven chromosomes between each of the three plants and 12 chromosomes in the species with the lowest number are certainly suggestive facts.