36 Transactions. 



suitability for the station. At any rate, the chance for natural selection to 

 effect anything here is very remote, although the competition is powerful. 



The number of true rock-plants in New Zealand is comparatively small ; 

 but, on the other hand, a great many xerophytes, and even mesophytes, are 

 encountered on dry rocks, but the latter are epharmonically modified during 

 their individual development. 



Even hygrophytes may gain a footing, as already seen in the case of 

 Hymenophyllum, nmltifidum. The most striking and truly amazing case is 

 that of the kidney-fern (Trichomanes reniforme Forst. f.) and Hymeno- 

 phyllum sangutnolentum Sw., which grow in the full blaze of the sun upon 

 the lava of Rangitoto Island, Auckland Harbour. The fronds of both, 

 as T saw them on a hot summer's day, were dry and curled up so as to 

 appear dead, but Mr. Cheeseman informs me that in winter the kidney- 

 fern covers the rocks with its translucent fronds, and that those of summer 

 are not dead at all. It seems evident that in this case the protoplasm of 

 these ferns must behave similarly to that of many lichens, and this will be 

 an epharmonic adaptation. The question arises, does such a power lie latent 

 in these ferns as normal rain-forest plants, ferns which cannot tolerate a 

 drying wind or a hot sun and dry atmosphere ; and, if so, how can it have 

 possibly come about ? Probably the porous rock contains a good deal 

 of water, and the air is usually not dry. Although I do not think that 

 any modification through the struggle for existence takes place amongst 

 rock-plants, yet this case shows that one cannot tell but that the most 

 unlikely species might settle in certain stations, and so inaugurate a new 

 line of descent, no matter how the evolution be brought about. 



In closed formations the struggle for existence between individuals is 

 very keen. As I write, in my garden, in a bed crowded with indigenous 

 plants, two rapidly growing and far-spreading Chatham Island herbs have 

 encountered, and one (Pratia arenaria Hook, f.) is rapidly replacing the 

 other (Cotula Muelleri T. Kirk), a happening quite in accordance with the 

 fact that the former plant is one of the most widely spread of the Chatham 

 Island plants. Reduced to its ultimate factors, the struggle is chiefly one 

 for nutriment in its widest sense, as Clements has shown (1905, p. 286) ; 

 there is little actual destruction of one plant by another, though they func- 

 tion indirectly by cutting off light, using up nutritive salts, &c. In some 

 cases the greater part of the struggle takes place amongst the young plants, 

 and it is on their adaptations, which may differ much from those of the 

 adult, that the establishment of the latter depends. This is specially evident 

 in those heteroblastic species already dealt with which have ecologically 

 different forms in their different stages. In a forest the conditions for 

 the seedling and sapling trees are very different from those to which the 

 adults are exposed. A favourable variation which might preserve a seed- 

 ling in the struggle with its environment would possibly have little to do 

 with the imperative demands of the adult. Small outward modifications 

 of a very few individuals could hardly be preserved in the dense growth 

 of saplings* in an upland forest of Nothofagus cliffortioides Oerst. The 

 chief requisite of success here is rapidity of growth, f a physiological 



* The saplings may grow so closely that one can hardly foice a passage through 

 them. 



f The case described in my little book, " New Zealand Plants and their Story," 

 of a species of Eucalyptus overcoming the eminently aggressive Leptospermum scoparium, 

 through its more rapid growth, both germinating at the same time, is instructive in 

 this regard 



