(1.) General.—An “irregular mat” best describes the growth-form taken by this species. It seldom forms a “pure mat”—i.e., a mat consisting entirely of its own vegetative growth—but grows on old consolidated terrace where many plants thrive, some of which are introduced species—e.g., Trifolium repens, Sagina procumbens, Hypochoeris radicata, Holcus lanatus, Cerastium glomeratum. Indigenous plants occurring among its mat are, amongst others, Hydrocotyle novae-zelandiae var., Anisotome aromatica var., Geranium sessiliflorum var. glabrum, Gnaphalium collinum, Plantago spathulata, and several small species of Carex and Luzula, together with various mosses. When other plants occur to any extent among the mat it is difficult to distinguish the Raoulia itself; in such cases it does not strike the observer as a distinct individual mat, but its erect branchlets, often widely separated, appear as separate plants struggling with their neighbours.
The appearance presented by the mat is that of a number of short, erect, greyish-white branchlets, each with two opposite rows of leaves. These branchlets are all that can be seen of the plant, and they grow vertically upwards among the mosses and other low-growing vegetation of the terrace. R. Monroi can hardly be said to exist as a separate mat—certainly not as an entity, as in the case of, say, R. Haastii; but it, along with various other small plants, forms a thick plant-covering to various parts of the old terrace.
(2.) Filling-material.—This plant resembles R. subsericea in that its stems do not merely trail over the surface of the substratum, but are well buried beneath it. In no case are any main stems visible on the surface: they creep among the humus-laden soil at a depth of from 0.5 cm. to 2 cm. or 3 cm. Hence it can be seen that this plant cannot possess any true
Fig. 10.—Diagrams of transverse section of stem of Raoulia Monroi, showing formation of stereome in pericycle.
filling-material. R. Monroi is really a plant with creeping and rooting underground stems, such as is found in Cotula perpusilla and certain other plants.
(3.) Coloration.—The general colour effect of the mat is a silvery grey. This is most obvious in a mat with the branchlets fairly close together and predominating over the intermingled moss and other low herbage. The greyness is due to the dense tomentum on the leaves. In winter the greyish colour is slightly suppressed, owing to a development of anthocyan in the leaf-margins.
(4.) Morphology.—(a.) Stem.—The stem is wiry, creeping and rooting. The main stems are horizontal and covered more or less with humus. The colour is a light brown, and the exterior is smooth, as the cortex does not fall away from this species so early as in the various species already described.
The branchlets have a flabellate form, with distinctly distichous leaves. In this respect they stand alone among the types considered, and, indeed, among the whole genus. They average about 1 cm. in length and 0.4 cm. in breadth. At least half the branchlet is clothed with the strongly conduplicate leaves. The branchlets are by no means compacted together, so that the mat hardly presents a “surface” in the ordinary sense. The flabellate form of the branchlets is accentuated by the recurving exhibited by the leaves.
Transverse sections of a young stem show the same appearance as in the other species of Raoulia; indeed, the differences between the young stems of all the species are but slight.
In an old stem secondary growth soon commences, and, as in the other Raoulias, the pith soon becomes lignified.
A peculiar feature of the stem is the mode of growth of the bands of stereome-fibres in the pericycle. As soon as secondary thickening has well begun certain groups of cells in the pericycle begin to lignify, and this lignification extends tangentially until it forms a complete cylinder (fig. 10). The stereome groups commence opposite the primary vascular bundles. This stereome-cylinder connects on to the secondary wood at certain points. These points number from four to six, and are opposite the primary medullary rays. The cortex suberizes from the exterior inwards and falls away gradually.
(b.) Leaf.—The leaves are oblong, with parallel edges and bluntly rounded tip, and arranged in two rows on the branchlets. The basal portion sheathes a part of the stem and the base of the leaf next above it. Both surfaces are covered with a dense white silky tomentum, especially the inner (upper) surface. The leaves are folded inwards along the midrib, and the dense mass of tomentum on the upper surface entirely fills the groove formed by the folding of the leaf. Owing to the apparent distichous arrangement of the leaves, there is no terminal rosette, as is so characteristic of the other Raoulias.
The proportionate amount of tomentum in the terminal bud is shown in fig. 11.
The contour of the leaf in transverse section is V-shaped, with the space between the arms densely filled with tomentum.
The leaf-anatomy is as follows:—Epidermis: Cells on upper surface flatter than below. Cuticle thinnish, same on both surfaces. Stomata on both surfaces; normal; sunken on lower surface, raised on upper. Hairs usual Raoulia type. Anthocyan in a few isolated cells in some leaves; in others it fills all cells. Chlorenchyma: Cylindric cells right round leaf; very dense at margins; two cells deep, except at midrib, where layer is single. Nearly every cell contains a large oil-drop. Water-tissue: About three layers of roundish cells; very few intercellular spaces; scanty chlorophyll. Vascular bundles normal.
(c.) Root.—Much as in R. subsericea.
(d.) Flower and Fruit.—Capitula 3 mm. long and about 1.5 mm. wide. Involucral bracts in three to four series. Florets from fifteen to twenty, the peripheral females the most numerous. Cypsela oblong, puberulous, pappus-hairs copious and slender.