114 ADAPTATIONS. OECOLOGICAL CLASSIFICATION sect, iii 



cited Myrtus bullata in New Zealand, Lippia involucrata and Plumeria 

 alba in the West Indies^, Salvia, Stachys aegyptiaca, Pulicaria and 

 Urginea undulata in the Egyptian desert, ^ also Vicia Cracca in Europe. 



The lie in all the cases mentioned above is attained by means of 

 torsions, folds, and curvatures that take place only during the develop- 

 ment of the individual ; hence, in all kinds of plants which assume 

 the shapes here described, the lie of the leaves varies with the nature of 

 the habitat. Exposed to sunlight, drought, or wind, the leaves become 

 more erect, or have their faces more vertical, or become more crumpled, 

 than when either in the shade or in a humid habitat where the air is moist. 

 This is the case with Calluna, Juniperus communis, Lycopodium Selago 

 and L. alpinum.^ The leaves of Tiha argentea on which hot sunlight 

 falls expose their edges to the light, but the remaining leaves present their 

 fiat faces.* 



Hereditary profile-lie is met with in Austrahan phyllodinous acacias, 

 the blade-hke petioles of which have their faces vertical, but bear no 

 lamina ; also in many plants with flattened or winged stems, or with decurrent 

 leaves, as in Baccharis triptera in Brazil, Genista sagittalis, Muehlen- 

 beckia platyclada, Carmichaeha austrahs, and species of Colletia. These 

 forms of shoots are usually aphyllous ; stem replaces the leaves. In 

 this connexion must be mentioned the ensiform leaves of Iridaceae, 

 Tofieldia and Narthecium. 



IV. INVESTING ORGANS IN THE CONTROL OF TRANSPIRATION 



It is evident that transpiration will be very materially reduced when 

 the transpiring surface is clothed by air-containing bodies, in and between 

 which the air is so firmly lodged that its circulation is obstructed.^ This 

 method is adopted in various ways by many land-plants.^ 



A. Investing Hairs. 



In regard to hairiness the contrast between hydrophytes and xerophytes 

 is especially marked : the former are glabrous, the latter often clothed 

 with grey or white cottony and woolly hairs, or by ghstening silky hairs ; 

 the optical effects are connected with the presence of air in and between 

 the hairs. Only dead air-containing hairs are fitted to perform the 

 function in question. In form, these hairs are extremely diversified.'' 

 It has long been known that species which are elsewhere glabrous become 

 hairy in dry places, and that hairy species become more hairy in dry 

 than in moist sites, as is exemplified by Ranunculus bulbosus, Polygonum 

 Persicaria, Mentha arvensis, and Stachys palustris ; moreover, etiolated 

 potato-shoots are nearly glabrous in moist, but hairy in dry air.^ Woolly 

 hairs coat many plants growing on rocks in Mediterranean countries 

 (Corsica,^ for instance), in the dry bushlands of the West Indies, in the 

 desert, steppe, or alpine situations. ^ The most thickly felted plant 

 perhaps is Espeletia,!^ one of the Compositae, Hving on high mountains 



> Johow, 1884. ' Volkens, 1887, 



' See illustrations in Warming, 1887. ' Kerner, 1887-91. 



* See Haberlandt, 1904, p. iii. ' See Burgerstein, 1904, p. 208. 



^ See illustrations in Kerner, 1887-91. * Vesque et Viet, 1881. 



' Rikli, 1903. '" See Lazniewski, 1896; Gobel, 1889-93, Bd. ii. 



" See illustrations in Gobel, loc. cit. 



