OUR NATIVE FLORA.

Auckland Star, Volume LV, Issue 188, 9 August 1924, Page 27

OUR NATIVE FLORA.

A BOTANIST'S JOTTINGS

ON TJTE DUNES. MARGUERITE *■ C ROOKES, M.A. Away cut on ' <c "T" n ena-t of both jTort'n and South i-l.w •' ■ we lind many a region "here V. ■■■ Mi-r.- U bounded to landward by m-:: ir.-j Imi interminable nules of barren m:kl hills. At first sight. nothing could appear in.ire and dull than tho?o n: i i-n.n.nw sand dunes. There is littio l-,;-. iai ■• -n on them—at any rate nc.ir th- -m *h"re, and anyone who has had tin' ini.-f..rtuno to plough through tin in li>r iiii;. Icnstli of timeon a hot day, «.m;1.1 marvi-1 how suuh wastes could cup)-rt any j l:ii.i life at all. Yet »i!K. i-'i fun..' riiiuls, hiid heat notwithstanding. t!i. dunos Lunc boon

most cffcvtiwly -oLmhsim] by plants, although on the iiti.-iable ones there are ' still to he n-i;i i<r mnre bare patches than vegetation. In tins tho sand dune.differ from, s.'.y. a kauri forest. In the kauri forest eyery available si-rap of B paco is occupied. 'Hutu are always more plants thai, there, is room for. Competition relentless ami unceasing. Puch a condition <-i things botanist* call a "closed" of plants. But out on the dun- il is different; there j is always unlimited >puo»- for any plant I hardy enough f> :-''-'' '< "P- Tl 'is con-j ditio'n is known as nn "open ,, association of plant*, it probably happened originally in this way. (>rmin plants i unable to comp.'to Miv.-i-ssfully for tho • fertile placid -■! the earth have been j "left behind."" a.- i , »m', in the stnu;gle ' for existence nml been compelled to betake them^hr* to tho wastes mid deserts. Such are the dune plant?, and it is interesting to spp how. having onco established those hardy j colonists maintain themselves in defiance j of the wind nnd sand. \ An Unstable Heritage. The dominating plants of the unfixed dunes are the pinguo (Scirpiio frondosusl, a seiljio, and the san<! ! gTass (Spinifex hir-utuM. ;i moniber of i the grass family. Both adopt a tussock form of growth, b'.u whereas pingao has leaves about two feet loii£ and frequently go!di>n brown in colour, Spinifev has leaves about nineteen inches long and of a silvery preen hue. But ;tp;irt from minor differences both have tiio same general habit of growth, and meet their difficulties in raiu-h the same way. The most u-wiMe enemy both have to face is the dr;ftin£ sand, which would exterminate the average plant in a very . short time hv the. simple process of burying it alive. Now pingao and Spinifex avoid this unpleasant contingency by a method that is at onco simple and effective. They send out lons creeping underground stems which root at intervals and at the same time put forth branches bearing the leafy heads for tussocks, that we see on the seashore. As the sand accumulates the stiims are Bpeedily buried, but what becomes of the leafy heads? They are quite safe, for the branches bearing them have r, .u----veloped the convenient habit of growing to keep pace with the piling sand! As the sand deepens, then, the branches simply '"add a cubit to their stature" and triumphantly bear their tussock heads up into the safe refrion of air and Bunlight. This method of prowth. of course, has the effect of binding the eand together to a remarkable extent. Indeed the interior of the ilune becomes a network of underground stems, branches, and roots, and we see at once why 6uch plants have earned for themselves the title of sand-binders. But tho plant reaps a further benefit from this growth habit. By it the plants are un- ' able to produce new plants vegetatively (i.e., without producing seeds and flowers), and although they use the seed , method too, it presents considerable diffi- I culties, as the unstable dunes are anything but a safe nursery for seedlings. Further Complications. But having successfully outwitted the drifting s anrl our sand-binders are by no means at the end of their troubles. In summer the sun beats down mercilessly Upon the unsheltered dunes and the surface of the sand becomes intensely hot. The fierce winds cause excessive evaporation, and moreover, since they are laden with stinging Eand grains, leaves would Epeedily become lacerated were they lot suitably protected. Now if we examine a tuft of the silvery sand grass we see that the leaves are of two kinds. | The outer ones are shorter and broader . at the base and simply serve as pro- j tectors. The ordinary leaves are some ; 19 inches long and "are very flexible,' strong and ltathery. They are armoured both within and without to enable them to withstand drought and wind. Within there is a special protective tissue of thick walled ceils giving strength to the leaf and preventing loss through evaporation. Without, the surface of the leaf is covered with fine silky hairs which give the plant its silvery appearance. These Berve a particularly useful pur- j pose by protecting the minute breathing porea through which evaporation takes place. They probahly also protect the plant from "the ba/1 effects of too strong light. Evaporation is further hindered by the fact that the margins of the last half or third of the leaf curve so that a tube is formed. Now let us consider the comrade of the silvery sand grass, the pingao. Its means of circumventing its enemies are very similar, but it has no special protecting leaves, and instead of silky hairs . it indulges in a sticky resinous covering as a meane of protection. The colouring of its leaves is tfomewhat remarkable. Underneath they are dark glossy green, while on top they are orange or red. This is probably 'because the illumination on the upper surface is very vivid. Now all green plants need light, but it is possible to have too much of a good thing. Therefore the plant hinders the entrance of certain rays of light by adopting red or orango colouring matter. A Diverting Seed Head. Of course both plants are dependent on the wind for the scattering of their Keds. The cfced head of Spinifex is a i most curious arrangement. It consist 3 ' of a large number of "seeds" joined together at a common centre. Each is provided with a spine about five inches '°ng, and the whole forms a globose head about a loot in diameter. Released from the parent stem it gops rolling and flopping along the -and on its long spines W all the world like a living insect. Its wanderings are only terminated when it falls to pieces The Maoris were quick i to notice there queer wandering seed heads, and put them to a most original *> s e. Sometimes when coming along tho beach tirod in the evening, they ] would catch smne and sending them rolling along the beach before them, i start oil in pursuit. According , £9 the rules tho runner must never allow i himself to be outdistanced. By this means j "l<* reached lioiuo in excellent tims. |

and to some extent forgot their weariness n tho interest of keeping the view. 1-or suck seed heads will invari:j £»» °" » ««* spurt and lake a v h them TK JUSt a3 ° nc C ° me3 U P 111 them. Tins entertaining form of borne coming i a unfortunately denied to most Southerner., a 3 Spinifex grows only in tne northern parts of the South Island the w r 7?nT m °, n Sllnd bindl "fe- P lint is the Nru; Zealand spurge. Uis about 3 foot high. with fleshy stalklosa leaves ahnut ~ inches long. When broken it pives.out a milky juieo. But the most hOHUtiful of the sand binders ia undoubt--0(1 ly tho native shore convolvulus It form* mats often several square, yards in extent. Tt comes as a pleasing "relief to the eye. wilh its kidney-shaped, dark groen f'.eshv leaves, and its lovclv pale Iliac flowers often an inch in diamrtcr. The four plants mentioned above are the moM important of the sand binding fraternity. But on the dunes we have also sand collecting and sand tolerating plants, and in a later article it will be shown how by studying nature's methods man can transform the useless and often dangerous sand dunes, into harmless and sometimes productive portions of his heritage.