170 Transactions. 



of this character must have been comparatively rare. The species of 

 Cassinia {Compositae) are quick-growing shrubs of cricoid form, tolerant of 

 considerable drought, and bearing in abundance seed of high germinating- 

 power, which can be transported rapidly over considerable distances by 

 the wind. * 



The association under consid(3 ration contains a variety of the coastal 

 Cassinia fulvida as its dominant member. Other shrubby members are 

 Discaria toumatou, Hymenanthera dentata var. alpina, Leptospermum sco- 

 parium var., Corokia Cotoneaster, Gaidtheria depressa, Styphelia Colensoi, 

 and Dracophyllum uniflonim var. 



The association occurs on ground formerly occupied by low tussock 

 grassland, where, through burning the tu.ssocks and subsequent grazing, 

 bare ground suitable for invasion by the Cassinia has been provided. The 

 shade and shelter furnished by the last-named encourages the establishment 

 of the other shrubs. The erect shrubby members of the association grow 

 in clumps or as single plants, and the interspaces consist of the original 

 tussock association more or less modified. Some of the species of the 

 latter are : Blechnum penna ynarina, Poa Colensoi var., Festuca novae- 

 zealandiae, Acaena Sangvisorbae var. pilosa, Viola Cunninghaynii, Pimelea 

 prostrata var., Styphelia Fraseri, Celmisia longifolia var., Raoidia subsericea, 

 Microseris scapigera, and Senecio bellidioides var. glahratus. 



Should the Leptospermum become dominant, such an association can 

 be rapidly transformed into manuka thicket, or, on the other hand, with 

 increase of Cassinia, many of the species mentioned above may be sup- 

 pressed. 



(b.) Discaria (Wild-irishman) Thicket. 



This is the " Discaria shrub steppe " of Cockayne and Laing,* a suit- 

 able enough term, but we think it best to abandon the word " steppe " 

 altogether in New Zealand phytogeography, because there is no consensus 

 of opinion amongst ecologists regarding its usage, so that formationsf of 

 very different ecological relationship s{ are called " steppe." 



The association consists, so far as shrubs are concerned, almost en- 

 tirely of the spinous, semi-divaricating Discaria toumatou (see foregroimd 

 in Plate XV, fig. 1), of an average height of, say, 1-2 m. In true thicket 

 the shrubs touch or grow into one another, but frequently this association 

 is more or less open. Clematis marata may be fairly common as a liane. 

 Other shrubs of the neighbourhood may be present here and there, but 

 they are of no moment. 



The association is extremely constant in its distribution throughout 

 the South Island, except west of the Southern Alps, and, when its dark 

 mass is seen at a distance, indicates dry river-terrace and those stony fans 

 where streams issue from their gorges. Eventually grass tussocks and 

 some of their accompanying plants, especially those of most xerophytic 

 structure, become established in the open spaces between the shrubs. 



* Trans. N.Z. Inst., vol. 43 (1911), p. 349. 



t The term "formation," as used by me, has a much wider signification than 

 " association," and is used to include such associations as are virtually ecologically 

 similar. Thus the whole rain-forest of New Zealand is one formation made up of many 

 associations which differ from one another floristically, but if ecologically, then only 

 to a very limited extent. So, too, low tussock grassland, swamp, and river-bed are 

 ecological units each containing more than one floristic unit. To compare the above 

 phytogeographical conceptions with those of taxonomy, the formation represents the 

 genus and the association the species. — L. C. 



t See E. A. Riibel, Journ. of Ecology, vol. 2 (1915), pp. 233-35. 



