ROCK-PLANTS. 79 
Rock-plants may be divided into those which are fixed to the 
actual surface of the rock and those which must commence their 
existence in a crevice or hollow where more or less soil has accu- 
mulated. The former class consists of algae, lichens, mosses, and 
liverworts; the latter embraces the seed-plants, the ferns, and 
certain club-mosses (Lycopodium). As the soil of the rock-face, 
hollows, or crevices increases in amount through decay of the 
vegetation the conditions less and less resemble those of an early 
stage of settlement, and an association may arise through biological 
succession having little to do with rock-conditions. Naturally, too, 
there are great differences between the associations of dry and wet 
or of sunny and shady rocks, while even apparently dry rocks 
may contain no small amount of water. Rocks readily weathered 
favour plants; in New Zealand their chemical nature is usually of 
little moment, though a few indigenous plants have, so far, been 
seen only on limestone—e.g., the lime-spleenwort (Aspleniwm obtusatum 
var. anomodon), the rock-anisotome (Anisotome Enysii), and A. patula. 
The serpentine rocks of the Mineral Belt in Nelson also have a 
selecting-power. 
Considering lowland rocks alone, the total number of species 
occurring on them throughout New Zealand is about 180, distributed 
amongst 43 families and 95 genera. With regard to their growth- 
forms, shrubs and herbs are nearly equal, and make up about 62 per 
cent. of the total; ferns come next in number. Only 20 of the 180 
species are purely or almost rock-plants; the remainder are largely 
drought-enduring plants of other formations—i.e., considering dry 
rocks only. 
The following species are more or less common on lowland rocks 
generally : The two species of New Zealand flax; the bush-lawyer 
(Rubus australis); the manuka (Leptospermum scoparium); the 
- snowberry (Gaultheria antipoda); the tall mingimingi (Leucopogon 
fasciculatus); the common koromiko (Veronica salicifolia); the 
broad-leaved poa (Poa anceps), in the North Island; species of 
piripiri (Acaena Sanguisorbae, various forms); the wild-irishman 
(Discaria toumatou), but this latter is not found in the North 
Auckland Botanical District or on North Island rocks in general. 
Coming now to details, on certain North Island, Nelson, and even 
Marlborough rocks the otherwise perching kahakaha (Astelia Solandri) 
may form pure colonies. In the East Cape Botanical District shady 
