Pegg. — Ecological Study of New Zealand Sand-dune Plants. 157 



3. Poa caespitosa. 



(a.) Habitat. 



Found, on active dunes, often just inland to the foredune ; also at 

 times in dune-hollows. Confined to the dune area. . 



(b.) Growth- form. 



A grass forming close yellowish-green tussocks, 1^—3 ft. high. Very like 

 Festuca littoralis in external appearance, but can be distinguished by the 

 inflorescence and less rigid leaves. 



Leaves narrow, so strongly involute as to be nearly terete, smooth, pale 

 green or yellowish, ending in fine sharp points. 



Inflorescence a panicle, fine, lax ; stalks slender ; branches few, in dis- 

 tinct clusters. 



(c. ) Leaf -anatomy. 



Leaf-margins meeting above midrib. From the small opening between 

 the margins to the midrib extends a narrow fissure, with a furrow on each 

 side of the midrib, reaching more than half-way to the dorsal surface of 

 the leaf. 



Epidermis : Exposed surface — elongated rectangular cells alternating 

 with smaller cells ; walls thick, undulating ; no stomata ; thick cuticle. 

 Inrolled surface — cell-walls thinner i;han on exposed surface, elongated 

 in surface view ; stomata frequent between the bands of subepidermal 

 stereome, regularly arranged with stomatal clefts parallel with leaf-axis ; 

 subsidiary cells present. Stomata sunk beneath the surface. Epidermal 

 cells rounded, and with outer wall much thickened ; many epidermal 

 cells smaller than the ordinary ones, and prolonged into simple hairs with 

 thick walls, forming a fairly close covering to the inrolled surface of the 

 leaf. 



Chlorenchyma arranged in bands, alternating with fibro-vascular bundles 

 and stereome. Cells relatively small, polygonal, close-packed, undifferen- 

 tiated, thick-walled ; air-spaces beneath stomata ; the chlorenchyma bands 

 reach the inrolled surface, but are usually separated from the exposed epi- 

 dermis by stereome. 



Stereome well developed, in thick bands above and below the vascular 

 bundles, extending to both surfaces ; stereome extends all along the 

 exposed epidermis. 



Fibro-vascular bundles arranged regularly, alternating with chlorenchyma 

 bands, of typical monocotyledon structure ; two large pitted vessels, a few 

 smaller spiral or annular vessels, and a lysigenous cavity ; sheath of colour- 

 less parenchyma enclosing mestome sheath with thickened inner walls. 



(d.) Conclusion, 



Poa caespitosa shows the following xerophytic characters : Tussock form, 

 involute leaf, protected surface hairy ; stomata on protected surface only, 

 and sunken ; homogeneous chlorenchyma of thick-walled polygonal cells, 

 and well-developed stereome. 



It is interesting to note the extra wall-thickening of the chlorenchyma 

 as compared with that of the apparently more xerophytic Festuca litto- 

 ralis. Poa caespitosa is a characteristic plant of tussock-steppe, and not a 

 special dune-plant. 



