20 Transactions. 



(I).) Raoulia Haastii. 

 (a.) Habitat. 



Raoulia Haastii occurs only on terrace grades 2 and 3. Its comparative 

 slowness of growth prevents its gaining a footing on grade 1. Its cushions 

 grow either among the boulders on the surface of the terrace or else at the 

 edges or banks, where it grows down over the edges, forming huge pulvinate 

 masses (Plate IV, fig. 2). This plant does not occur at all on terrace proper. 

 It does not encroach even on the edges of old terrace, as does R. hitescens, 

 but appears to die away before even the external limit of grade 3 terrace 

 is reached. 



(ft.) Life-form. 



(1.) General. — This species is the most conspicuous of all the cushion- 

 plants on the river-bed ; it is the cushion-plant par excellence of this area. 

 Its large cushions, bright-green in summer and chocolate-brown in winter, 

 are very conspicuous objects. The cushions are large, in some cases over 

 1 m. across, and 12 cm. deep. Its periphery and surface are irregular. The 

 surface is thrown into numerous mounds and hollows, which were formed 

 primarily by the plant covering, when young, obstacles of various kinds, 

 such as boulders and driftwood. These irregularities have been retained 

 in the adult condition, and give the cushion its characteristic irregular 

 contour. 



Though the gereral contour is irregular, the actual surface is smooth, 

 due to the compactness and uniformity of the branchlets. The cushion is 

 of the many-roott 7 type. In adult plants there is no dominant central 

 root, but a multitude of adventitious roots arise from the creeping stems. 



The arrangement of the upper branches in tiers, such as was noted in 

 the case of R. hitescens, is apparent here also. In some cases six tiers can 

 be made out before a considerable deposit of humus appears in the centre 

 of the cushion. The cushion is as compact and as difficult of penetration 

 as that of R. Ivstescens. 



(2.) Filling-material.- — This varies with the age of the cushion. When 

 young the growth-form is really a mat. In young flat mats it consists chiefly 

 of sand, but as the mats increase in depth more and more humus makes 

 its appearence. In old cushions there is a very marked amount of filling- 

 material in the centre of the cushion, consisting of a rich humus mixed with 

 sand. The general colour of the filling-material is black. The leaves die 

 away rapidly behind the terminal rosette, and become black. 



(3.) Coloration. — The summer colour of R. Haastii is a sap-green. But 

 the most conspicuous coloration is in the winter, when the whole cushion 

 becomes a rich chocolate-brown with a tinge of red. As the winter colora- 

 tion of this species was so remarkable it received special attention. Close 

 inspection of the rosette showed that the tips and edges of the leaves were a 

 reddish brown, but where central leaves showed they were a yellowish green. 

 Behind the rosette the leaves die away and become brown, and the tips 

 of these dead leaves showing here and there on the surface assist in giving 

 the general brownish colour to the cushion. 



Microscopic examination showed that the epidermal cells are filled with 

 anthocyan, which is densest at the angular edges and tips of the leaves. 

 Beneath the epidermis is the chlorenchyma. The yellow-green of the chloro- 

 phyll, covered with the pinkish-red of the anthocyan, gives the brownish 

 effect so characteristic of the winter habit of the plant. That the brownish 



