THE MALLOWS AND RIBBON-WOODS 257 



one of the difficulties that has presented itself to the 

 investigator of the New Zealand trees and shrubs, is, that the 

 intermediate stage is often simpler than the seedling form, 

 and thus the usual law seems to be reversed. This puzzled 

 Dr. Diels considerably. In reference to Pseuclopanax, he 

 states, that the most remarkable thing about the leaf changes 

 is, that in all similar cases there is a progression from simple 

 to more complicated forms, but here, on the contrary, the 

 high degree of differentiation of the young foliage suffers 

 reduction later on. Hence, he considers, that in this case, 

 recapitulation of the ancestral history is not probable. 



Dr. Cockayne's Theory. 



Eecently, however, Dr. L. Cockayne has put forward a 

 theory to account for these curious metamorphoses." Within 

 our limits, it is not possible to discuss this interesting 

 hypothesis fully, though it is cei'tainly one of the most 

 remarkable and suggestive ever put forward with regard to 

 our native plants. 



It had already been shewn by Dr. Diels, that an unusually 

 large percentage of the trees and shrubs in the New Zealand 

 Flora are xerophytic in structure (y. Introduction, p. 41, also 

 Veronica, Aciphylla, Discaria, etc.). This type of plant 

 structure seems to indicate, that the past climate of New 

 Zealand was much more arid than at present. The vegetation 

 of the Canterbury Plains in particular, is of a desert type. 

 Such a belief is supported by the geological evidence. 

 Captain Hutton has pointed outt that during the Pliocene 

 period, the Southern Alps were much higher than they are 

 now. He considered that the land surface of New Zealand 

 then extended eastward to the Chathams, and southward to 

 the Auckland Islands. Under these circumstances the 

 climate of the interior would approach to the continental in 



*Trans., Vol. XXXIH., p. 277 tTrans., Vol. XXXII. p. 182. 



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