24 Transactions. 



branchlets can offer unlimited resistance to the wind. Its firm margin and 

 general robustness of growth ; its small leaves with thick cuticle and 

 sunken stomata ; its densely packed branchlets ; its filling-material with 

 adventitious rootlets entering it — these structural features all point to a 

 plant of xerophytic habit. 



. , , T (E.) Raoulia subsericea. 



(a.) Habitat. 



This species is essentially a plant of the old stable terrace : it is found 

 only there and on the lower slopes of the bordering hills ; it does not 

 approach the edge of the terrace which borders on the river, but usually 

 is well away from the bank. Large quantities of this species grow among 

 the Festuca tussocks on the terrace, and also in the low tussock grassland 

 generally. 



(ft.) Life-form. 



(1.) General. — R. subsericea forms large, very flat mats. It has trailing 

 stems like R. tenuicaulis, but is much stouter. The horizontal stems root 

 copiously, and give off very short vertical branches, which end in the 

 branchlets. The general contour is flat ; the surface is rather rough, owing 

 to the breadth and large size of the rosettes, these being larger than in any 

 of the raoulias considered above. The mats are of irregular outline, and 

 their margins are closely interwoven with the surrounding herbage. Indeed, 

 it is difficult to find a " pure " mat, as so many other plants grow up through 

 the middle of it. In spite of this, however, the mats as a whole often occupy 

 a considerable area, some o.f them being at least 1-5 m. across. The depth 

 varies from 2-5 cm. to 4 cm. There is a general lack of compactness, and 

 there are very large spaces between the branchlets as comparer! with the 

 two previous species. 



(2.) Filling-material. — There is practically no filling-material. The 

 leaves die away behind the rosette, but remain attached to the branchlet. 

 Dead grass leaves and other plant debris may collect among the branch- 

 lets and stems, but owing to their comparatively wide distances apart 

 there can be no " sponge " effect produced, and consequently no growth of 

 adventitious rootlets into the centre of the mat. 



(3.) Coloration. — -In summer the general effect is a sage-green, due to 

 the green leaves edged and tipped with grey tomentum. In winter the 

 edges and tips of the leaves develop anthocyan, and the general colour 

 effect of the mat is a very light brown. 



(4.) Morphology. — -(a.) Stem. — -The stem is much stouter than in the 

 other species, some of the main stems being 2-5 mm. in diameter. It is 

 usually buried in the humus which here forms the common covering of the 

 old terrace — the common growth-bed, indeed, for all the plants thereon. 

 Hence R. subsericea, whose branches ramify through this surface-soil, cannot 

 be said to have a filling-material of its own. 



The branchlets are all free, not closely compacted, and form the only 

 part of the plant which comes above the surface of the substratum. They 

 vary in length from 0-75 cm. to 2 cm., and their average breadth (including 

 leaves) is 0-6 cm. They are densely clothed with leaves, which die away 

 and hang down on the lower two-thirds of the axis. Their anatomy need 

 hardly be described. The whole stem-structure is very similar to that of 

 Raoulia tenuicaulis, except as regards the rather larger size. 



