The so-called chromosome-races of Cardamine pratensis and Nasturtium officinale.

Abstract

IN his recent article on “Plant Chromosome-Races and their Ecology in Great Britain”1, Dr. G. Haskell devotes a paragraph each to lady's smock (Cardamine pratensis) and to watercress (Nasturtium officinale agg.). So far as Cardamine pratensis is concerned, he omits to mention the work of Hussein2,3, who has made by far the largest study of the distribution of the two chromosome-races of this plant in Great Britain. Haskell states that in Great Britain, as in Sweden, the form with the lower chromosome number (2n = 30) is characteristic of drier conditions than the form with the higher chromosome number (2n = 56). This was found by Hussein, who says : “The ecological difference found by Lovkvist holds good in most of the cases recorded ; for example, Prof. R. D'O. Good, who kindly provided material from Dorset, noted particularly that the large plant, now found to have the low chromosome number, occurred in quantity on the damp roadside banks characteristic of Marshwood Vale, whereas the smaller darker-leaved one (2n= 56) grew in wet meadows”. It should also be noted that the chromosome number of Cardamine pratensis from Merton was found by Lawrence4 to be 2n = 30 (thus agreeing with counts made by Lovkvist5 and Hussein2,3 and with unpublished counts by myself for the lower chromosome number form) and not 2n = 32 as stated by Haskell, although Lawrence did suggest that it may have arisen from 2n = 32 by chromosome fusion.