L. Cockayne and Foweraker. — Plant Associations at Cass. 171 



(c.) Leptospermum {Manuka) Thicket. 



This belongs to the formation hitherto called " manuka heath " by 

 L. Cockayne. It seems to lis best to abandon the term "heath," partly 

 because it is of loose application, and partly because in many parts of New 

 Zealand the dominant shrub reaches too great a height to permit comparison 

 with the heaths of Europe. At the same time, where climatic and soil 

 conditions combine to produce a low, more or less uniform growth of 

 L. scoparimn, " heath " is far from being an unsuitable designation. 



At Cass fairly wide areas occupied by manuka are not uncommon. 

 How far these are primitive we do not know, but some seem to bear a fairly 

 primitive stamp. The relation of Lejytospermum scoparium var. to the 

 surrounding vegetation at Cass requires detailed study. 



{d.) River-terrace and Debris Scrub. 



On the sides of gullies cut by streams through a fan, on the faces of 

 river-terrace throughout the Waimakariri Kiver basin generally, of which 

 the Cass area forms a part, and on the otherwise bare stony debris of the 

 hillside v>here weathering has led to an accumulation of rather large stones 

 there are dense scrubs of a similar floristic composition, but differing 

 according to habitat in the relative proportions of the important members. 

 These scrubs owe their special physiognomy largely to the presence of the 

 divaricating growth-form in abundance, and to the green- or it may be 

 glaucous-leaved species of Veronica. Should Veronica dominate — a frequent 

 happening in many parts of montane and subalpine New Zealand — we have 

 a " Veronica scrub." These scrubs are usually of considerable density. 

 The shrubs grow intermixed, and lianes may bind them still more tightly 

 together. The divaricating shrubs afford an extremely striking example 

 of convergence, belonging, as they do, to several distinct families — e.g., 

 Pittospontm divaricatum (Pittosporaceae) , Discaria toumatou (Rhamnaceae), 

 Aristotelea fruticosa (Elaeocarpaceae), Hymenanthera dentata var. alpina 

 (Violaceae), Corokia Cotoneaster (Cornaceae), Coprosma propinqua var. 

 and C. parviflora var. (Rubiaceae), and Olearia virgata var. (Compositae) . 

 If this convergence, which we certainly consider epharmonic, were to be 

 dealt with not merely from one plant association, but from the New 

 Zealand region as a whole, the figures would be not merely eight species 

 belonging to seven families, but fifty-six species belonging to nineteen 

 families and twenty-three genera ! 



The scrub of shaded gullies is closely related to forest, and with the 

 appearance of Nothofagus clijfortioides as a member forest may be considered 

 in process of formation. But the scrub of steep, stony debris, on the other 

 hand, is one of those rather rare communities that is at the same time an 

 initial and climax association on a par with those of shingle-slip, dry rock, 

 and the Epilobium association of river-bed. 



According as certain species are dominant, so is the facies of the asso- 

 ciation under consideration more or less altered. But we do not consider 

 such change great enough to warrant the establishment (except in the 

 case mentioned below) of more than one association for Cass. Besides 

 the shrubs already mentioned, the following are generally present : Bis- 

 caria toumatou, Gaultheria rupestris var., Veronica salicifolia var. communis, 

 and Veronica Traversii var. Olearia avicenniaejolia var. is occasionally 

 present. If the ground is wet, then Veronica buxifolia var. odora may 

 become so important as to dominate, in which case certainly the asso- 

 ciation has changed its character, and may be named V. buxifolia scrub. 



