308 Transactions. — Botany. 



land that the change wrought by constant burning can be 

 properly estimated. Nor is it burning alone, as already 

 pointed out, which brings about changes in the vegetation, 

 but rather burning plus the attacks and trampling of 

 animals. As to the effect of these two causes combined 

 upon the plant-covering, no plant is so instructive as Phor- 

 mium tenax. This, once extremely common nearly all over 

 "the clears' of Chatham Island, as shown before is now 

 almost extinct. How this came about seems worthy of a de- 

 tailed explanation, since misstatements regarding the causes 

 which lead to the eradication of P. tenax have been circu- 

 lated so often as to be accepted by the scientific world as 

 fact. Thus Wallace writes: " White -clover (Trifolium 

 repens) spreads over all the temperate regions of the world, 

 and in New Zealand is exterminating many native species, 

 including even the native flax (Phormium tenax), a large plant 

 with iris- like leaves, 5 ft. or 6 ft. high " (52, p. 29). 



If we consider the stations in New Zealand where P. tenax 

 grows, we find that in several of them white-clover can only 

 grow with difficulty or not at all. Such are rocks, very dry 

 river-terraces, sand-dunes, and very wet swamps, this latter 

 a most characteristic station. Moreover, the reclaimed Phor- 

 mium swamps in which white-clover is now established and 

 Phormium eradicated have usually been artificially drained, 

 and the Phormium itself constantly set fire to, thus bringing 

 about a very different state of affairs for the white-clover to 

 become established than an undrained swamp. 



But the introduced-plant factor and the fire factor would 

 be of no avail to destroy Phormium and lead to its replace- 

 ment by a comparatively insignificant plant did not stock eat 

 its leaves with avidity, especially the young and comparatively 

 tender ones which spring from its rhizome after burning, 

 with the result that, the growing-point being destroyed again 

 and again, the rhizome finally rots and the plant dies. This 

 is what has happened to the Phormium in Chatham Island. 

 After fire its succulent leaves are almost the only food avail- 

 able for the hungry stock ; they are eaten and the plant 

 perishes. So also every seedling that cannot establish itself 

 out of harm's way is destroyed. In the lowland swamps, out 

 of reach of the stock, young plants of Phormium may be occa- 

 sionally seen on the stems of Garex secta. With the drain- 

 ing of the swamps that haven of refuge will be gone, and Phor- 

 mium will only be met with on rocks and in shallow lakes, 

 where under the two opposite conditions there seems every 

 chance for two new species being evolved. 



In the place where Phormium originally grew there is no 

 reason why white-clover, or any plant whatsoever that can 

 maintain itself against other competitors, should not re- 



