Pegg. — Ecological Study of New Zealand Sand-dune Plants. 159 



5. Scirpus nodosus. , . TT , . 



(a.) Habitat. 



Found in active dunes, commonly in manuka heath or sand-plain, also 

 in sand-hollows, at both ends of the beach. Also occurs on coastal rocks 

 and inland in heath river-bed, and occasionally steppe. 



(b.) Growth-form. 



Close, stifE, tussocks of rush-form, 1^ — 3 ft. high, of numerous stems. 

 Can be easily recognized by the inflorescence. Rhizome stout, woody. 



Stems erect, stiff, slightly flattened, ^-J in. in diameter, dull green, 

 functioning as leaves. 



Roots long ; root-hairs all along, rather long and sparse. 



Leaves absent, except for reddish sheathing scales at the base of the 

 stems. 



Inflorescence characteristic ; a head of spikelets towards the end of the 

 stem, head brown, solitary, globose, J-§ in. in diameter, spikelets numerous, 

 crowded together ; head appears lateral, owing to the presence of a rigid 

 bract, about 1 in. long, continuous with the stem. 



(c.) Anatomy. 



Stem a slightly flattened solid cylinder, consisting of epidermis, chloren- 

 chyma, and stereome, fibro-vascular bundles, and central pith. 



Epidermis : Cells above stereome bands rectangular, not much elon- 

 gated, cell-walls thick, those parallel with stem-axis undulate ; cells above 

 chlorenchyma rather irregular ; cell-walls not undulate ; frequent stomata 

 arranged parallel with axis, subsidiary cells present, thick cuticle ; stomata 

 slightly sunken. 



Chlorenchyma in a continuous cylinder beneath the epidermis, inter- 

 rupted on its outer side by bands of stereome ; all palisade tissue, several 

 cells deep, cells small and compact ; a relatively large air-space beneath 

 the stomata. 



Stereome in thick bands, regularly arranged beneath the epidermis, all 

 round the stem, forming ridges ; stereome bands somewhat pear-shaped in 

 transverse section ; peculiar processes from the stereome, probably thicken- 

 ings of cell-wall, are occasionally seen in the epidermis. 



Fibro - vascular bundles : Structure typical of monocotyledons, with 

 sheath of thick-walled cells and patch of thick-walled cells at the base of 

 the bundle ; bundles arranged in two or more rings, the outer ring of small 

 bundles, the inner bundles larger and more well developed. 



The centre of the stem consists of pith of large polygonal cells. 



(d.) Conclusion. 



Stem-structure is typically xerophytic, with thick cuticle, thick-walled 

 epidermal cells, compact palisade, and stereome. The absence of leaves and 

 the photosynthesizing stems are markedly xerophytic characters. 



In connection with Scirpus nodosus a few. words must be said about the 

 tussock form. Cowles* says, " The leaves of most grasses and sedges grow 

 so close together that the assumption of a position transverse to incident 

 light is mechanically impossible. . . . Leaf vertically or parallelism to 

 the incident light results obviously in minimum lighting for any individual 



* " Text-book of Botany," vol. 2, Ecology, p. 544. 



