Megional Distribution of the Cape Flora. 245 



favour transpiration. Vines* points out " that, cceteris 

 paribics, the transpiration is proportional to the surface of a 

 leaf, though, as might be expected, the activity of trans- 

 piration is very difierent in leaves of different structure ; 

 thin herbaceous leaves, for instance, transpire much more 

 freely than do those which are fleshy or coriaceous." Hence 

 the small, excessively coriaceous leaves of these plants 

 without much spongy parenchyma are thoroughly suited to 

 the climate. We may even, I think, go a step farther, and 

 say that the physical conditions have produced this form. 



The much-branched stunted condition seems to me only 

 an intensified state of what we may see even in this country 

 when we compare trees grown in open exposed places with 

 those grown in woods. With regard to leaves, certain 

 observations which are not yet extensive enough for publica- 

 tion, as to the variation in size and texture of the leaf in the 

 same species in different habitats, strongly incline me to 

 believe that the smallness, cuticularization, and want of 

 spongy parenchyma in the leaf all follow directly from such 

 conditions.t 



The large number of flowers is probably in correlation 

 with the greatly branched condition, while their small size 

 has probably something to do with the small size of the leaf. 



I must mention here, however, that there is in these 

 districts an extraordinary number, both of species and indi- 

 viduals, of certain peculiar Coleoptera and Hymenoptera which 

 are the main agents of fertilisation, and are distinguished by 

 their very small size. These belong chiefly to the genera 

 Anisonyx (specially A. ursus and longipcs), DicMlus {D. 

 sirapliciptes and dentipes) in Coleoptera, and the very small 

 Hymenoptera Ccratina, Odynerus, and others. Still, however, 

 the general similarity of these plants seems to me to give us 

 data from which to gather the influence of physical con- 

 ditions. 



What speaks very strongly in favour of this view is the 

 fact that such plants are only found in such situations as 

 those mentioned above. Immediately one reaches, in an 



* Lectures on tM Physiology of Plants, Camliridsje, 1886, p. 105. 



t Here also cf. Vines, loc. eit., p. 107, and Hohnel Jdhrb. f. Wiss. Bot., xii. 

 1880, Stahl Yeivx. Zeits., Bd. xvi. 1882, Pick. Botan. Ccnfmlblatt, Bds. xi. 

 and xvi., various memoirs by Costantin, Grosglik, Wiesner, &c. 



