258 PLANTS OF NEW ZEALAND 



character. The plains to the east of the Southern Alps 

 would be subjected to a great range of temperature, and 

 great drought. Dr. Cockayne ingeniously explains the 

 developmental stages of the present lowland plants, by 

 reference to these past conditions. Obviously, only those 

 plants that could develop protection against the rigours of the 

 climate, would survive the test of such an environment. 

 When the land again sank, the climate would become moister 

 and more insular. Xerophytic plants, if still plastic, would 

 again assume their original form, or, if unable to do this, 

 would become extinct, or retire to the shingle-fans, dry rocks, 

 and river-beds, where we now find them. 



Let us now apply this hypothesis, to explain, if possible, 

 the forms through which Plagianthus betulinus passes in its 

 development. A seedling of this species goes through three 

 distinct stages in reaching the mature form. (1) The stem 

 and branches of the young plant are erect, the leaves are of 

 definite shape, somewhat similar to those of the mature stage, 

 but with truncate or cordate bases. ('2) The seedling, now 

 grown into a shrub, changes its appearance completely. The 

 branches become long, drooping, twiggy, flexuous, and of a 

 red-brown colour. The leaves are very much reduced in size, 

 and very variable in shape. The plant might now be taken for 

 one of the Cojjrosmas. None but a careful observer would be 

 likely to recognize in this unkempt twisted shrub, the young 

 form of the handsome beech-like tree. (3) The third or 

 mature form, already described, is a handsome, graceful tree, 

 with large, alternate, rather flaccid leaves. 



These forms, if Dr. Cockayne's theory is correct, represent 

 in order (1) the early Pliocene type, existing when the climate 

 was mild, before the elevation of the mountains ; (2) the 

 interwoven coprosma-like stage of the later Pliocene deserts ; 

 and (3) the mature form of the present day, which resembles 

 the early Pliocene type, as the climate has once more become 

 comparatively temperate. 



