14 Transactions. 



R. australis is of fairly wide distribution on the river-bed, and may be 

 found on all the grades except the old terrace. Indeed, it so resembles 

 young hairy forms of R. tenuicaulis that the latter could easily be mistaken 

 for it. As it does not form a distinct cushion, and is extremely prostrate, 

 it is unable to combat with taller plants ; hence its disappearance on 

 terraces above grade 3. 



(/?.) Life-form. 



(1.) General. — The growth-form of this species is a low, very flat mat, 

 much resembling that of R. tenuicaulis, with the usual centrifugal growth, 

 but with its main stems somewhat thicker than are those of R. tenuicaulis. 

 They are straggling, and do not produce a copious growth of intermediate 

 branches so as to form a close mat ; in young forms much shingle and sand 

 is visible between the branches. The contour is rather flat, but the surface 

 is very rough and uneven, due to the inequality of the branchlets and their 

 lack of compactness. 



Its rate of growth is rather rapid, though less so than in R. tenuicaulis ; 

 hence its margins are uneven and lax. A noticeable feature of this species 

 is its copious flower-production. Copiously flowered heads terminate nearly 

 all the branchlets in the flowering season, and when the fruits are mature 

 the whole surface of the mat is covered with the tufted pappus-hairs crown- 

 ing the fruits. 



(2.) Filling-material. — Owing to the thinness and looseness of the mat 

 this is practically non-existent. The branches and stems are clothed with 

 the light-brown remains of the dead leaves. A certain amount of coarse 

 debris is entangled among the stems in the centre of the mat, giving this 

 portion a darker appearance than the periphery. 



(3.) Coloration. — The general colour of the mat is greyish, due to the 

 copious white silky hairs on the leaves. In winter the edges of the leaves 

 develop anthocyan, which gives a slight brownish tinge to these parts, so 

 that the whole greyish appearance of the mat is modified by an elusive 

 pink hue. 



(4.) Morphology. — -(a.) Stem. — The stems have much the same appear- 

 ance as in R. tenuicaulis. They are prostrate, terete, wiry, and of a light 

 brown. Copious roots are given off from the lower surface, thus producing 

 a distinct dorso- ventral appearance. 



The branchlets are short (0-3 cm. to 0-7 cm. long), and clothed through- 

 out their whole length with leaves, which die away only at the very base. 



The young stem has its general anatomical structure much the same 

 as in R. tenuicaulis, except that the pith has not so great a proportional 

 diameter. 



The old stem is much the same as in R. tenuicaulis, except in the 

 following features: (i) Less pith in proportion, (ii) Greater growth of 

 secondary wood ; the elements are arranged in more regular radial rows ; 

 the walls are thicker, and there are more numerous pitted vessels, which 

 also have a greater lumen, (hi) More sclerenchymatous fibres on the peri- 

 phery of the phloem opposite the primary vascular bundles ; these are 

 probably pericycle fibres, (iv) The endodermis has thicker walls, and 

 the cells are shorter tangentially. 



In other respects the secondary growth of the stem is the same as in 

 R. tenuicaulis, both as regards lignification of the pith and suberized cortex, 

 which is cast off as far as the endodermis. 



