156 Transactions. — Botany. 



jurious influences. In consequence of its altitude, and the 

 lack of shelter, the worst foe of Haastia is the intense cold of 

 winter. Its adaptations to secure protection from the cold 

 are remarkable and very obvious. The whole structure is 

 such as to diminish radiation, and to keep out icy wind and 

 snow-water. It is low-gi'owing, very compact by reason of its 

 method of branching, and forms a rigid mass which is im- 

 penetrable both from the sides and the top. Each branch is 

 covered with leaves adpressed to the stem, closely packed 

 together, which persist on the stem a great length of time, 

 forming a covering for the plant down to the ground. Little 

 heat IS lost, too, by radiation from the leaves, for these are 

 reduced considerably in size and overlap each other, so that 

 no part is exposed but the tip. Each leaf, too, is covered, 

 in parts that would else be exposed, by a very dense wool, 

 which, as a non-conductor, is as well fitted as sheep's wool for 

 retention of heat. By these means neither stem nor leaf is 

 free to radiate heat. The adaptations that keep the plant 

 warm in wmter serve to prevent excess of heat in summer : 

 the non-conducting wool prevents the plant-tissue from being 

 scorched up in this arid situation, as also excessive loss of 

 water by transpiration. 



The mountain wind-storm is another great foe. The wind, 

 sweeping down the mountain-sides, finds on the desolate slips 

 nothing to check its fury, therefore in winter there is the 

 storm-wind and in summer the fiery north-wester. The 

 plant is helped to contend against these foes by its low-grow- 

 ing habit and the stoutness of its stem, due chiefly to the 

 large development of sclerenchyraa ; and it is so compact that 

 no wind can enter it to damage its branches. 



Haastia 2}idvinaris Ivdn no need to fear what would be to 

 other plants a formidable foe — the shifting of the shingle. Its 

 root is strong owing to sclerenchyma ; and the combined 

 strength of the branches is so great that they can withstand 

 the injurious influences of heavy masses of shingle. 



Haastia pidvinaris would he exposed to drought in summer 

 did it not send downi a long tap-root, which is also of advan- 

 tage in firmly fixing the plant in the shingle. 



The adaptations of the plant to prevent loss of heat, the 

 closeness and rigidity of the cushion, the closely adpressed, 

 hair-covered nature of the leaves, are equally active in pre- 

 venting assimilation, transpiration, and respiration. Yet the 

 leaves, though tightly packed and warmly clad, have still 

 means of performing these functions. Whereas the lower 

 part of the leaf is closely pressed to the stem on its inner 

 surface, and is covered by other leaves on its outer surface, 

 the leaf-tip is free, and is modified for the better performance 

 of the leaf-functions. 



