XIV] ROLLED LEAVES, ETC. 145 



rapidly put forth thin leaves during the rainy period, and 

 these fall by the time of drought. Other plants escape the 

 dangers of drought by assuming the fleshy, cactoid habit 

 and store water in their fleshy shoots, but form no leaves. 

 It is, therefore, especially in the case of perennials which 

 retain their leaves during the dry season, that the adapta- 

 tions we are concerned with are found, and if we meet 

 with a case where, in an arid climate, such leaves appear 

 to be typically thin, flat, and with large surfaces, &c., the 

 probability of further study of its habits revealing some 

 special adaptation as yet undiscovered is shown by ex- 

 perience to be great. 



Many leaves are rolled up, the edges being curved 

 upwards in some, such as Fescue, Stipa, Ammophila and 

 other grasses, downwards in others, such as Empetrum, 

 Heaths, Ling, and other Ericacece, Epacmdem, Rosemary, 

 &c.; and it is suggestive that many of these plants are 

 evergreen and live on moors, alps, sea-shores and such 

 places where the air is often dry for long periods and 

 where cold dry winds sweep their surfaces at intervals. 

 It is further suggestive that such leaves are reduced in 

 area by the rolling, have thick cuticles, and that their 

 stomata are few and are situated on the concave surface. 

 Some of these leaves are erect, e.g. the Grasses, others 

 closely overlap, e.g. the Heaths, and most of them are 

 covered with a waxy bloom on the exposed surfaces, e.g. 

 Ammophila, or with a tomentum of hairs on the covered- 

 in stomatal surface, e.g. Rosemary, &c.; all of which 

 peculiarities appear to be adaptations to reduce the 

 dangers of excessive transpiration. Indeed, this sug- 

 gestion receives support from the observation that some 

 of these leaves unroll themselves out flat in dull and 

 moist weather e.g. Ammophila and close up again in 

 drought. 



w. IL 10 



