Cockayne. — Ecological Studies in Evolution. 39 



full-sized trees of Weinmannia racemosa L. f. Sophora tetraptera J. Mill, is 

 restricted in Chatham Island to the forest on limestone near the shore of 

 the Te Whanga Lagoon, though elsewhere in New Zealand it can grow 

 abundantly on rock similar to that of the rest of Chatham Island. The 

 accompanying trees are the same in the limestone forest as in forest of the 

 island generally, but it is evident the volcanic rock of the remainder of 

 the island favours the other trees, which do not allow Sophora to become 

 established. Or it may be that Sophora is a comparatively recent arrival.* 



The distribution of certain species shows that epharmony is by no means 

 so complete between plant and habitat in some cases as one might expect ; 

 or, in other words, that a plant can live in a position for which it is not 

 perfectly fitted. Thus, Mr. R. G. Robinson, Superintending Nurseryman 

 for the South Island, informs me that the dominant tree of the Tapanui 

 Forest, Nothofagus Menziesii Oerst., cannot be grown in the adjacent State 

 nursery, although N. jusca Oerst., a comparatively rare plant in that 

 locality, can be grown with extreme ease ; and yet I have seen N. Menziesii 

 growing quite well on the flanks of Ruapehu as an isolated tree in the open.f 

 The slow growth of many indigenous trees as compared with introduced 

 species is another case in point. On Antipodes Island the plant-associa- 

 tions are not distinguished by their different floristic components so much 

 as by the relative abundance of the different species. This word " abund- 

 ance " shows that all are not equally suited for each station, but that if a 

 plant settles down on ground not specially fitted for its requirements it may 

 be able to hold its place, the struggle for existence notwithstanding. So, 

 too, with various stations on the Auckland Islands. A highly specialized 

 species may thrive under conditions that might be deemed impossible. 

 Such a case is the already mentioned hygrophytic almost aquatic Tricho- 

 manes reniforme on the sun-baked rocks of Rangitoto. Here are a few 

 more examples : Crassula moschata Forst., a coastal halophytic herb, is 

 one of the pioneer plants in the heavily manured ground just abandoned 

 by penguins on the Snares Island. Colobanthus muscoides Hook, f., an 

 herbaceous dense cushion plant growing normally on coastal rocks, is an- 

 other early-comer on the above manured ground, but as conditions become 

 favourable for less manure-tolerating plants both are replaced, tussock 

 moor or Olearia forest being the climax association. Metrosideros scandens 

 Sol., a root-climbing woody forest-liane, grows in some places on rocks 

 close to the sea. G-riselinia lucida Forst. f., so far as I am aware always 

 either an epiphyte or a rock-plant, can be cultivated with ease as an 

 ordinary garden-shrub. 



The presence of closely related species side by side in the same associa- 

 tion has a strong bearing on the mutation question, for it is reasonable 

 .to suppose with Leavitt (1907, pp. 210-12) that if natural selection, or 

 even epharmony, is responsible for species-making, only one type will be 

 present. As Leavitt writes, " Mutation breaks the species, and moment- 

 arily at least must give a polytypic aspect to the group within a specific 



* H. H. Travers (1869) was of opinion that this tree was a very recent arrival, 

 especially as an old resident, Mr. Hunt, did not know it, and as he found a seed on the 

 shore of Pitt Island. I have given my reasons for be eving it an ancient constituent 

 of the flora (1902, pp. 270—71), and have seen no reason to change my opinion. 



f The case may not be as strong as it appears, since the seedlings are shade-loving, 

 whereas those of N. fusca can tolerate far stronger light. There is also a fine tree in 

 the dry Christchurch Domain, where the climate is much more unsuitable for indigenous 

 forest-plants than Tapanui. 



