Variation occurring in Biscutella laevigata. 



13 



consequence of tufts of stiff hairs borne on the leaf teeth, or the 

 glabrous character may be even more pronounced, the leaves being 

 destitute of hairs except for a few bristles on the petiole. 



Reichenbach* and Boreau,f on the other hand, make no mention 

 of a glabrous variety; the former describes the leaves as strigose 

 hispid, the latter as pilose or hirsute. 



The occurrence of glabrous and hairy varieties within the limits of 

 a single species is not unknown ; but in those cases previously 

 investigated it has been found that this divergence of character can 

 be correlated with some sensible inequality in the environment, and 

 that where similar conditions constantly prevail there is uniformity 

 of type. A familiar example of this kind of adaptation is afforded 

 by the well authenticated case of Polygonum amphibium which was 

 noticed by Linnaeus ; % this plant is invariably glabrous when 

 growing in wet ditches or pond.s, but it produces leaves more or less 

 downy if for any cause the ponds or ditches dry up. By placing the 

 land variety under appropriate conditions, Hildebrand§ was enabled 

 to convert it into the typical aquatic form — a sufficient proof that 

 both tjpes are rightly referred to the same species. Nor is this the 

 only instance that can be adduced; Linna3us|| observed a similar 

 variability in Plantago coronopus and other plants ; he also records 

 that Lilium Martagon assumes a glabrous habit when cultivated 

 in gardens, and that Thymus serpyllum becomes more or less hairy 

 when growing on sea- coasts. It was further noticed by Moquin- 

 Tandon*" that plants occurring at high altitudes were generally 

 more hairy than these found in the plains. More recently, a large 

 number of comparative experiments have been undertaken by 

 Bonnier,** who enumerates a list of species in which, among other 

 changes, a greater or lesser increase in general hairiness resulted 

 from transplantation from valleys to high mountain slopes. Again, 

 Warmingft states that smooth plants occupying dry areas become 

 hairy in moist situations, and, similarly, those which otherwise are 

 somewhat hairy, under the latter conditions exhibit this character 

 in a more marked degree ; he quotes, in support of his statement, 

 Polygonum persicaria, Ranunculus bulbosus, Mentha arvensis, and 



* 'Flora GrermanicaExcursoria,' p. 660 ; also ' Icones Florae Grermanicse,' in which, 

 the leaves are figured, as hairy all over. 



f ' Flore du Centre de la France,' t. 2, p. 56. 

 t ' Philosophia Botanica,' par. 272. 



§ 'Bot. Zeit.,' 1870, p. 20; also Volken's 'Jahrb. des Konigl. Botanischen 

 Gartens zu Berlin,' vol. 3 (1884), p. 6. 

 || Loc. cit. 



1 ' Pflanzen-Teratologie,' p. 62. 



** 'Revue gen. de Bot.,' 11,1890; also 'Ann. des Sci. Nat.,' Ser. VII, t. 20, 

 p. 225. 



ft 1 Lehrbuch der ckologischen Pflanzengeograpkie,' p. 187. 



