L. Cockayne and Foweraker. — Plant Associations at Cass. 175 



(5.) EocK Associations. 



Dry rocks can only support a scanty assemblage of plants consisting of 

 highly specialized, drought-enduring forms, or of species that can ephar- 

 monically alter their form. Such, to cite some of the species belonging 

 to the first category found in such a habitat at Cass, are : Colohanthus 

 acicidaris, Pimelea Traversii, Veronica epacridea, V. tetrasticha, and Heli- 

 chrysum Selago var. But the fissures, hollows, and crevices of rock readily 

 become filled with soil, and so provide a habitat more easily colonized, 

 where many plants belonging to less xerophytic stations can thrive. When 

 such positions are in the shade, or are so situated as to receive an abundant 

 supply of water, there will be a rich florula, but many of the species will 

 have little to do with rock conditions. The following lists include only 

 those species which are either true rock-plants or are commonly found on 

 rocks where soil has accumulated, though also belonging to other associations. 



{a.) Montane Rock. 

 Most of the species belong equally to other associations. The following 

 list does not discriminate between the plants of dry rocks and those of 

 moister rooting-places : Blechnum capense var., Poa Colensoi var., P. caespi- 

 tosa var., Festuca novae-zealandiae, Luzula campestris var., Colohanthus 

 acicidaris, Geum parviflorum, Carmichaelia subulata, Coriaria sarmentosa var., 

 Discaria toumatou, Aristotelia fruticosa, Viola Cunninghamii, Hymenanthera 

 dentata var. alpina, Pimelea Traversii, Leptospermum scopariiim var., Epi- 

 lohium melanocaulon, Angelica montana, Anisotome aromatica var., Corohia 

 Cotoneaster, Gaultheria rupestris var., Styphelia Fraseri, Dracophyllum uni- 

 florum var., Veronica salicifolia var. communis, V. Traversii var., Coprosma 

 propinqua var., Wahlenbergia albomarginata, Olearia avicenniaefoUa var. 

 Helichrysum hellidioides var., H. Selago var., Cassinia fulvida var. montana. 



(b.) Siibalpine RocJc. 

 Here rocks on Mount Sugarloaf are alone considered. The habitat is 

 dry, and frequently wind-swept. The altitude is not sufficient for certain 

 species more or less common on rocks of the neighbouring higher mountains. 

 The following is a list of the species : Podocarpus nivalis, Aciphylla Colensoi, 

 Anisotome aromatica var. stunted, Dracophyllum rosmarinifolium, Styphelia 

 Colensoi, Suttonia nummularia, Veronica epacridea, V . tetrasticha, Celmisia 

 spectabilis, Senecio Bidwillii. Almost certainly Colobanthus acicidaris and 

 Pimelea Traversii are present, but they are not mentioned in our notes. 



(6.) ElVER-BED. 



Broad stony river-beds, over which anastomosing streams wander, are 

 a frequent feature of the South Island of New Zealand. They carry a 

 fairly uniform vegetation, which exhibits certain well-defined phases in 

 harmony with topographical and biological changes. The bed proper is 

 that portion of the stony area occupied by the streams, and liable at any 

 time to be flooded and its plant-covering to be eradicated ; it is, in fact, 

 a habitat of extreme instability. Popularly included in the term " river- 

 bed " is the more stable ground, formerly the flood-plain, on either side 

 of the bed proper, and this we likewise include in our treatment of river- 

 bed. Throughout the South Island the vegetation under consideration has 

 a similar life-history. 



First of all, there is the extremely open plant -covering of the unstable 

 bed, which, owing to the instability of the substratum, does not pave the 



