76 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY, 



The consideration of the significance of the various protective 

 devices adopted by alpine plants presents many difficulties of this kind. 

 One can rarely say with any degree of certainty against which factor of 

 the alpine climate any particular device affords protection. As we 

 have seen, everything in the alpine surroundings and conditions favours 

 transpiration, or the giving off of water vapour from the leaf surface. 

 In spite of the abundance of atmospheric precipitation plants growing 

 on the sun-baked slope of an Alp with, very probably, moraine stuff 

 or scree as a subsoil, and with 50 per cent, less water vapour in the 

 atmosphere than is the case on the lowlands, are necessarily compelled, 

 as a condition of their existence, to adopt measures for the purpose of 

 retaining a supply of moisture m their tissues. Many are the 

 peculiarities of alpine plants to which the discharge of this function 

 has been attributed. Sedums and Sempervivums, which necessarily 

 grow in dry places, have thick, fleshy leaves capable of storing water 

 in their tissues. The Edelweiss, the Anemones, Senecio incanus, 

 and the Antennarias are covered with a fine woolly tomentum. 

 Rhododendron ferrugineum has minute brown scales on the under 

 side of the leaves, Saxifraga Aizoon, S. cotyledon, and *S'. longifolia, 

 and allied species are thickly encrusted with lime on the edges 

 of the leaves. It is suggested that all these features are devices protec- 

 tive against excess of transpiration. According to Keener, most of 

 them may also be regarded as a protection against excessive illumina- 

 tion. "Through these structures," he says, "two birds are killed 

 with one stone. All contrivances which keep off too glaring sunbeams, 

 and thereby hinder the destruction of chlorophyll, at the same time 

 diminish transpiration."* It is not, therefore, surprising if alpines in 

 th© course of their adaptation to the less brilliant light and moister 

 atmosphere of the British Isles undergo a considerable modification in 

 respect of those features of their development which may be regarded 

 as special adaptations to their native climate. Accompanying this 

 modification, there are also the structural changes already referred to in 

 the elongation of the axes, and the increase in area of leaf surface 

 favoured by the less brilliant light and less rapid alternations of ex- 

 tremes of temperature prevailing in the lowland climate. By way of 

 explaining the foregoing the following quotation from a treatise on 

 Plant Physiology by Professor Leclerc du Sablon, published only this 

 year, may be of assistance, being an up-to-date expression of opinion 

 by a botanist of undoubted qualifications on the problems presented by 

 the peculiarities of alpine vegetation : — ' * Parmi les caracteres des 

 plantes alpines, quelques-uns sont precisement ceux qui sont determines 

 par un ^clairement plus intense, toutes les autres conditions etant 

 egales d'ailleurs. Tels sont I't^paisseur des feuilles, I'importance du 

 tissu en palissade, I'abondance de la chloropliylle, I'epaisseur de la 

 cuticule, le nombre des stomates, le d6veloppement des fibres. 



" La s^cheresse de Pair dans le meme sens que I'eclairement et 

 * Kerner, op. cit. vol. i. p. 392. 



