Cockayne. — Ecological Studies in Evolution . 17 



{?.g., Scirpus frondosus Banks & Sol., Coprosma acerosa A. Cunn., Gunnera 

 arenaria Cheesem., Euphorbia glauca Forst. f.). 



An interesting case is that of Lycopodium ramulosum T. Kirk, a plant 

 forming extensive patches on moors in the west of the South Island and 

 Stewart Island, the sporophylls of which are absent or scantily produced 

 in shade plants, but extremely abundant in those growing in bright light. 



Many young trees in the forest assume a special form with a slender 

 main stem and few branches, which are confined to its upper portion. 

 Similarly, the xerophytic fern Pteridium esculentum Cockayne becomes in a 

 dim light a scrambling liane. An example observed by Mr. H. Carse and 

 myself was growing amongst tall, slender Leptospermum scoparium on Reef 

 Point, north-west Auckland. Some of the fronds were more than 3 m. in 

 length. Pinnae were absent until the brighter light was gained. The final 

 portion of the rhachis was green and succulent, and the distance between 

 the pinnae 46 cm. These latter were still coiled up and quite rudimentary, 

 although the largest was 25 cm. long. The rhachis was twisted — i.e., it 

 showed a tendency to twine. 



Shade — and here probably comes in moisture in" the air — increases the 

 size of leaves, changes certain xerophytes into mesophytes : e.g., species 

 of Carmichaelia, Discaria toumatou. Podocarpus nivalis Hook., as may be 

 plainly seen from Plate IV, responds markedly to changes in illumination, 

 the shade form resembling P. totara much more than the species which it 

 really is. The specimens were collected within a few feet of one another. 



The lie of the leaf is regulated by the light. Olearia insignis Hook, f., 

 a shrub of dry rocks in Marlborough, arches its branches upwards to a sur- 

 prising degree, thus bringing its leaf rosettes into a suitable position with 

 regard to the light. This habit persists in plants raised from seed and 

 grown on flat ground. 



(c.) Wind. 



Wind is a most important factor in New Zealand. First comes the 

 '' wind-shearing " action, which is in part a physiological process ; it is 

 well marked in trees and shrubs of exposed positions, and may be frequently 

 seen in Podocarpus totara D. Don., Leptospermum scopariurn, Forst., and 

 many other plants. The prostrate habit is encouraged by wind ; but here 

 other factors may enter in, as cold and acid soil. Coprosma foetidissima 

 Forst. is usually a tall forest-shrub, but when a member of the tussock- 

 moor association of the Auckland Islands (Cockayne, 1909a, pp. 200, 201, 

 and 219) it is prostrate and twiggy. The prostrate form of Leptospermum 

 scoparium on the subalpine moors of Stewart Island is another and remark- 

 able example. Well-developed prostrate trunks are to be seen in Metro- 

 sideros lucida Menz. (Myrtac.) in the Auckland Islands, Stewart Island, and 

 the Southern Alps, and in Olearia ilicifolia Hook. f. (Compos.) in some sub- 

 alpine forests of the South Island. Reduction in size of leaves must often 

 be attributed to wind-action. 



(d.) Water. 



Plants of still or slowly running water are subjected to a fairly con- 

 stant environment.* Cotula coronopifolia L., as a land-plant, is a herb with 

 branched, prostrate, more or less rooting stems, the branches of which are 

 erect or semi-erect ; the internodes are short ; the leaves are rather 

 fleshy, more or less lanceolate in outline, and pinnatifid, lobed, toothed, or 

 sometimes entire ; the roots are, at most, of a moderate length. As a 



* Of course, the position of the plant with regard to the surface, the nature of the 

 substratum, and other factors exercise a considerable influence. 



