THE NATURAL SHRUBBERIES. 55 



however, the water-vapour passes from the leaves faster than it can 

 be replaced by the roots, the former will wilt, and in time the plant 

 would die of thirst. 



Many contrivances have been evoked to hinder this, and the form 

 of the leaves is in part an expression of the relation of a plant to its 

 water-supply. The heath and the subalpine-scrub plants noted below 

 show many interesting drought-resisting contrivances. Although a 

 leaf loses water principally through its minute pores, some may pass 

 away from the whole leaf-surface. To hinder this the surface is 

 specially thickened, or covered with water-resisting substances, such 

 as wax. 



Variations of leaf-form play an important part. Do away with 

 leaves altogether and the case is met. Carmichaelia australis, a 

 northern plant of the pea family, is leafless, but has green, flattened 

 stems, which can function as leaves. The almost leafless wild-irish- 

 man (Discaria toumatou) has developed rounded spines which, though 

 they serve likewise as leaves, offer much less surface than would long 

 green stems. The needle-like leaves of the dracophyllums not only 

 present little surface, but they are vertical, and so never feel the full 

 effect of the sun's rays, which together with dry air and high winds 

 have much effect on the rapidity with which a plant loses water. 

 Pomaderris phylicaefolia reduces its water-losing surface by recurving 

 the edges of its leaves. Olearia furfuracea has a mat of dense hairs on 

 the under- surf ace of each leaf. 



THE SUBALPINE SCRUB. 



In many places on the high mountains in New Zealand, especially 

 in a part where the rainfall is excessive, upon emerging from the 

 upper forest one is confronted with a formidable natural fence, many 

 chains in breadth, dividing the forest from the meadow land. On 

 certain mountains this belt is absent, or represented by stunted beech- 

 trees or isolated patches of shrubs. The above barrier, composed 

 of a thick and varied growth of shrubs, is designated the " subalpine 

 scrub," and if unprovided with a track is virtually impenetrable 

 (fig. 21). The shrubs, dense in themselves, have such wiry or rigid 

 branches interlacing into one another that no passage can be made 

 between them. In many places where it is impossible to crawl on 

 one's hands and knees beneath the close mass, the only alternative 

 is to walk upon the top. 



5 Plants. 



