Foweraker. — Mat-plants and Cushion-plants of Cass River Bed. 23 



the single central vascular bundle and the chlorenchyma is an aqueous 

 tissue of roundish or polygonal clear cells containing but few chloroplasts. 

 Vascular strand : Sheath of large clear cells. Xylem has a few scattered 

 vessels. Lateral branching bundles terminate in spiral tracheides among 

 the chlorenchyma. Phloem composed of normal sieve-tubes and companion 

 cells. 



Towards the sheathing base the character of the tissues changes. The 

 cuticle becomes thinner ; the stomata are not sunken ; the chlorenchyma 

 changes to ovoid and finally to rounded cells, and becomes ultimatelv 

 confined to a single layer just beneath the epidermis on the outer convex 

 surface, while the lower layer of chlorenchyma changes to tissue similar to 

 the water-tissue. The leaf-sheath consists of two layers of epidermal cells 

 near the thin margin, but its extreme outer edges consist of a single layer. 

 The epidermal cells all contain anthocyan (in winter). Behind the leaf- 

 apex on either side is a shallow depression lined with fine twisted hairs, 

 silvery white, and covered more or less with a mealy substance, possibly a 

 glandular secretion. In these depressions the cuticle is thin, and the hairs 

 arise from single epidermal cells. 



(c.) Root. — The roots are very long, wiry, dark brown or blackish in 

 colour, and rather free from tortuous twistings ; they are straighter than 

 in the previous species. From the branches below the third tier of branch- 

 lets copious adventitious roots are given off into the filling-material. 



The anatomy is much as in the previous species, but there is a greater 

 development of lignified tissue. 



(d.) Flower and Fruit. — The capitula are short (3 mm. long). In vomeral 

 bracts scarious, especially at edges ; obtuse at tips. Very few florets 

 (four to eight), about half the number being female. Achene slightly hairy, 

 with a long bimch of pappus-hairs, which are slender and not thickened 

 above. The capitula soon disappear, the involucre becoming detached 

 early, so that the surface of the cushion does not show any sign of flowering 

 later than February. In this respect it differs from the other species, 

 especially R. australis and R. sitbsericea, on which the involucres persist 

 throughout the winter. 



(y.) Formation of Cushion. 



The earliest stages have not been observed, but small plants forming 

 mats from 2 cm. to 5 cm. across occur on grade 2 and 3 terrace. The 

 growth is compact from the commencement, and the young mats are minia- 

 tures of the mature plants. The marginal growth is slow and even. There 

 are no long runners as in R. tenuicaulis, and no difference between the 

 branchlets and rosettes of the periphery and centre. The only difference 

 is that the marginal branchlets are less closely packed. 



(8.) Epharmonic Variations. 



In the Cass Valley this plant showed absolutely no variation whatever. 

 Growth-form, filling-material, branchlets, rosettes — all were alike in every 

 plant examined. Plants grown in a greenhouse at sea-level from March 

 to October showed a difference from those in the Cass Valley as follows : 

 Laxer growth ; more succulent stems and branchlets ; less compact rosettes ; 

 less xerophytic leaves — viz., thinner cuticle, leaves larger and more flexible. 



(e.) Conclusions. 



Raoulia Haastii illustrates in several ways the suitability of the cushion- 

 form to its habitat. Its rounded convex surface and densely packed 



