Foweraker. — Mat-plants and Cushion-plants of Cass- River Bed. 13 



growth in the spring, particularly in September ; (iii) this new growth 

 much greener and decidedly less hairy than that in the Cass Valley ; 

 (iv) general softness, succulence, and laxness of growth. 



(£.) Conclusions. 



R. tenuicaulis appears to be a plant fitted for a shingly or sandy sub- 

 stratum, where the water-supply is not too deficient. The structure of the 

 plant shows that it is not so strongly xerophytic as the other species of 

 Raoulia described in this paper. 



The structure of the stems is perfectly adapted to the habit of the plant. 

 They are thin and wiry, and the central column of strongly lignified tissue 

 lends strength. The stems can creep through sand, can withstand floods, 

 the dashing against them of sand and shingle, and the crushing effect of 

 boulders. Their wiriness imparts a springy effect to the whole mat, so 

 that it is not easily flattened or crushed by flood-sand or flood-shingle. 



The leaves show several xerophytic features, but the xerophytic 

 characters of the leaves of cushion-plants as a whole are dealt with 

 further on. 



The rapid growth of this plant, where energy is put into horizontal 

 rather than into vertical extension, enables it rapidly to clothe a barren area 

 with its mats. Its copious seed-production and the plentiful distribution 

 of the seeds enables its seedlings to establish themselves in the most diverse 

 places where a little moisture is available ; hence its early appearance on 

 embankments, cuttings, and other bare places. Further, its rapid growth 

 enables it easily to overtop any sand or silt that has covered its mats 

 during a flood. 



Its early peopling of the recently vacated bed proper does not mean 

 that it is suited to absolute desert conditions. This lowest grade of terrace 

 is also that nearest to the underground water-table, and consequently the 

 first to be benefited by a rise of the water-table. Where it grows on rocks 

 and railway cuttings it is found in those places which are exposed to a trickle 

 of water, due to a spring or other form of soakage. It does not occur on 

 the higher parts of the second-grade terrace, and not at all on the third 

 grade. Its non-appearance on terrace proper may be explained by the 

 fact that it cannot long brook competition with other plants. It readily 

 succumbs before the hosts of invading species, and then serves but to 

 provide a bed of humus. 



(B.) Raoulia australis * 

 (a.) Habitat. 



Along with R. tenuicaulis, several forms of this species are found on the 

 lowest grades of terrace. It may be said that R. tenuicaulis appears first 

 on grade 1 terrace, and R. australis next. It is to be understood, how- 

 ever, that R. tenuicaulis and R. australis are not the only plants which 

 invade the newly exposed shingle. Epilobium melanocaulon and E. peduncu- 

 lare vars. are quite a^ frequent inhabitants of the lowest grade, but they 

 do not concern this paper. f 



* The above name as applied here refers only to the " species " as it occurs at Cass, 

 and even there it is fairly polymorphic. 



t By Cockayne and Foweraker this association is called the " Epilobium association " 

 (1916, p. 176). 



