198 SUBANTARCTIC ISLANDS OP NEW ZEALAND. [Ecohjicnl fiohiiii/. 



sucli luxuriance of growtli wlien the wind factor is considered is indeed reniarlv- 

 able; but it must be remembered that the leaves of several are only summer-green, 

 while those of others are specially strengthened by powerful veins. The leaves of 

 the three species of AciphjUn are remarkably thick, stiff, and xerophytic in their 

 inner structure : all are divided, and those of A. antipodn and A. acutifnlin very 

 considerably. x\lso, where these plants grow luxuriantly there is considerable 

 shelter, and they decrease in size and become more prostrate or are altogether absent 

 in the most wind-swept stations. PkurophjiUnui Hookeri flattens its leaves to the 

 ground (fig. 13), and they are covered densely (Hi Ijoth surfaces with a mat of silky 

 hairs. The other two species of Pleurophi/l/uiii are tomentose on the under-surface. 



**** The Tussock Form. (Figs. 1 and 11.) 

 Equally with the cushion habit is the tussock, a well-known subantarctic life- 

 form, one particular species (Poa flabellafa, of the Falklands) being known as the 

 " tussock-grass." The form consists of the bunching-together of numerous grass- 

 like leaves or rigid stems, which, extremely close at the base, spread out above, the 

 apical portions frequently drooping to some extent. In the subantarctic province 

 the tussocks are confined to grasses and sedges (Carex), but in other parts of the 

 New Zealand region Restionacene, several genera of Cyperaceae, and even Liliaceae 

 have this habit. Usually the grass and sedge tussocks build up stout trunks out 

 of their dead culms, leaves, rhizomes, and roots, on the summit of which they grow 

 under a special edaphic condition of their own providing. These trunks may be 

 cylindrical or quite irregular in shape, and may reach a height of 1-5 m. Poa foUosa, 

 Poa litorosa. DanfJionia antarctica, Carex trifi,da, and Carex appressa are all trunk- 

 builders, but this habit is not invariable with them by any means. 



***** The Mat Fori)!, the CrecjiiiKj Form. 



The plants belonging to this life-form have spreading stems, which creep either 

 on the surface of the ground or just beneath it, in the former case giving off short 

 roots at the internodes. In some cases the plants form either spreading mats, 

 differing much in closeness, or dense patches. Examples are : Coprosma repem, 

 Nertera depressa, the species of Cotula, the two Asteliads, the Epilobia, Pratia 

 arenaria, CaUitriche antarctica, and Poa ramosissima. Plants in which the creeping 

 form is well developed have an advantage over those which are spot-bound, in 

 rapidly occupyin*^ new ground. 



****** The Tufted Form. 

 This consists of stems given off' from near one another and either erect or creep- 

 ing. Between erect tufts and tussocks, and indeed rosettes, it is only a question of 

 degree. The species of Scirpus and Gentiana cerina are examples. 



(iii.) Vegetative Parts. 



* Lea/. 



The great size of leaf of some of the most characteristic phints has been already 



discussed. Urtica australis, virtually a subantarctic species, and the endemic U. 



nucMandica* are also large-leaved. Many species have quite small leaves — e.g., 



* 1 am by no moans sure that this is distinct from Urtica australis. 



