Foweraker. — Mat-plant s and Cushion -plants of Cass- River Bed . 27 



touch those of neighbouring ones, while in other cases the leaves of the 

 branchlet are not in contact with anything. The contour is flat, but the 

 surface is most uneven, due to the unequal length of the branchlets. 



(2.) Filling-material. — In this species filling-material is practically non- 

 existent. A small amount of decayed leaves forms a loose humus at the 

 bases of the main branches. 



(3.) Coloration. — This plant shows greater stability in colour than other 

 members of the genus. During the summer the mat is of a light-green 

 colour, and this changes but little during the winter. The edges of the 

 leaves become very slightly tinged with anthocyan, and this is just sufficient 

 to give the slightest suggestion of brown to the mat. 



(4.) Morphology.- — (a.) Stem. — The stems are wiry, creeping, brownish 

 in colour, more or less covered with remains of the dead leaves, much more 

 slender than in R. subsericea, being from 075 mm. to 1*5 mm. in diameter. 

 Whereas in the latter species the stems are more or less buried in the humus, 

 in R. glabra they merely trail on the surface and interlace with each other 

 in the mat. Adventitious rootlets are given off as usual, but there is not 

 such a firm hold of the ground obtained as in other species. It is quite easy 

 to pull up large areas of the mat by grasping any portion of it, whereas in 

 most of the other species any such attempt removes only a small local tuft. 



The branchlets greatly resemble those of R. subsericea ; they vary in 

 length from 1cm. to 3 cm.. and. including the leaves, are 7*5 mm. in 

 diameter. Their axis tends generally to take up a vertical position, but 

 is not as strictly so as in the previous forms. Being much more lax and but 

 loosely in contact with neighbouring branchlets, they are capable of much 

 movement, and when a mat grows in the shelter of a dense bush or a large 

 stone the branches show strong positive heliotropism. 



The anatomy of a young stem, on transverse section, shows the follow- 

 ing structure : Epidermis very regular. Cortex of about four layers of 

 parenchymatous cells, with chloroplasts. Endodermis not so clearlv marked 

 as in other species. Vascular bundles, about eight primary bundles. Pith, 

 thin-walled parenchyma. 



The anatomy of an old stem as growth proceeds exhibits the following 

 changes : The cortical cells lose their contents and become flattened and 

 suberized. In old stems the cortex falls away as far as the endodermis, or 

 a laver or two outside it. The endodermis becomes much more stronslv 

 developed and conspicuous. In the early stages it is not too clearly defined 

 from the cortical tissues, but as growth proceeds its cells enlarge, become 

 barrel-shaped, and stand out distinctly from the roundish cells of pericycle 

 and cortex. Secondary thickening commences early, and small strands of 

 lignified fibres appear in the pericycle opposite the primary vascular bundles. 

 The pith commences to lignify at the initiation of secondary thickening. 



(b.) Leaf. — The leaves have very much the same shape as those of 

 R. subsericea, though somewhat narrower. Their length is about 3 mm., 

 and their breadth 0-75 mm. They have parallel edges, tapering for the 

 last quarter of the length to an acute tip. The base is slightly broadened 

 and clasps the stem. The midrib is visible as a groove on the upper surface, 

 but obscure on the lower. The leaf is glabrous, save for a small area of white 

 silky hairs on the dorsal surface, extending from the apex along the midrib 

 for a third of the length. 



The terminal rosette resembles that of R. subsericea, but is much smaller. 

 In forms growing in dry situations the leaves are erect, but in forms from 

 moist places the leaves are reflexed. The rosette of this species differs 



