318 PLANTS OF NEW ZEALAND 



similar spinescent bracts, guarding the flowers with veritable 

 chevaux de frise. No plant could be better defended 

 against the attacks of grazing animals, and the earlier 

 botanists naturally concluded that the purpose of the spines 

 was protective. One thing puzzled them. Why should 

 plants, which were indigenous to a land where no animals 

 browsed, be guarded by such terrible thorns ? There was no 

 satisfactory answer to this question, though Wallace" even 

 goes so far as to suggest that " they may have gained their 

 spines to preserve them from being trodden down by the 

 moas, which for countless ages took the place of mammals in 

 New Zealand." However, the trend of recent investigation is 

 to show that the spines are not protective, but the natural 

 results of modifications resulting from the struggle against 

 drought. 



Many New Zealand plants at some stage or other of their 

 existence are of a xerophytic type, (v. Introduction, p. 41) and 

 perhaps no better example could be found than Aciphylla^ 

 Why so many of our plants should be xerophytic is a puzzle 

 to botanists, but a fuller discussion of the question will be 

 found under Plagianthus betulinus (pp. 254-258). 



That the leaves should be reduced to spines in Aciphylla is- 

 especially remarkable, because the leaves of other members of 

 the family are often large, and well developed. Those, 

 however, of A . Colensoi and A . squarrosa are in the seedling form 

 quite flaccid and grass-like t, while, according to Mr. Cox of 

 the Chatham Islands, the leaves of A . Traversii are so soft that 

 sheep eat them greedily. On well stocked stations the plants 

 therefore suffer severely, and are soon exterminated. These 

 anomalies of leaf -form tend to show that the ancestors of the 

 genus Aciphylla were of a normal type. 



If further argument were required to show that the spinous 

 leaves of Aciphylla are really drought-forms, and not protective 



*" Darwinism," Colonial Edition, p. 433. 

 f Cockayne: Trans. XXXIII., p. 279. 



