a—is

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Theoretically, sand contains very bttle available plant-food ; but from analyses of soils in general very little is to be learnt regarding their nutritive qualities. So far as the New Zealand sands are concerned, it is surprising, if only there be shelter, what a variety of plants will thrive, including massive trees, and especially if water can be supplied ; but, as shown above, there may be more nutritive matter than is suspected. Massart (41, pp. 156-165) lays great stress on the effect of the above-mentioned lack of nutritive salts in producing poverty of vegetation and stunted growth of plants of sand-hollows in the Belgian dunes, supporting his views by most careful observations and soil-analyses. His statements regarding not only reduced growth in the land plants of the hollows, but in the aquatic plants of the dune ponds are of great interest, and suggest detailed examination of New Zealand material. In the immediate neighbourhood of the sea there will doubtless at times be a little salt on the surface, but it is now considered that the salt-content of dunes has been altogether overestimated. and that the soil has no excess of salt (see Kearney, 31, and Derbyshire, 126 a, p. 297). An analysis of New Zealand sands is wanted to settle the point, so far as our dunes are concerned. At any rate, many meadow-plants, which could not tolerate excess of salt — e.g., the daisy (Bellis perennis). white clover (Trifolium repens), &c. —grow on or close to the shore itself. On the other hand, the plants of dunehollows, where the ground-water is fresh and comes to the surface, are in part those of brackish water and salt meadows — e.g., Leptocarpus simplex, Selliera radicans —an interesting fact, since it demons! rates how these so-called halophytes are really not salt-demanding plants at all. (iv.) The Topographical Factor. As seen from the paragraph dealing with the general topography of the dunes in the geological section of this report, a considerable diversity of stations are offered for plants in the hills, mounds, sand-plains, and so on, so far as water-content, stability of surface, shelter, shade, and even soil are concerned. A dune itself offers quite different conditions on the windward and lee slopes as regards steepness, velocity of sand-motion, exposure to wind, depth of water beneath the surface, and firmness of the sand. The height of the hills and their relative position have, as already seen, a strong hearing on the erosive power of the wind. The relationship of the dune-area to the sea-shore—i.e., to the sand-supply —its position with regard to the sea, its relation to the prevailing winds, and the character of the underlying soil ; these matters have a strong bearing upon the nature of the. plant covering, ami must be especially studied when dealing with dune-reclamation. (v.) The Plant-covering Factor. Wherever there is a plant covering the force of the wind.is more or less broken, though adjacent tussocks or shrubs which are at some distance apart may lead to a wind-channel being formed, and consequent denudation. Where the plants arc not far apart, and occupy a patch of ground, even though there are bare spaces between them, the sand will not move, and within the plant zone the principal dune condition is eliminated, and xerophytes other than sand-binders can flourish. A plant covering, too, helps to conserve the moisture, and adds a little humus to the soil. This is of slight moment on the unstable dunes, but becomes of considerable importance in the hollows, and even on the hills after these become stationary. In fact, given a long enough period of repose, a soil is finally developed on which mesophytic species can settle. Generally the plants are far apart, and their presence does not hinder the settling-down of other species ; and this to some extent takes place, various European weeds, not dune-plants at all, entering into the association— e.g., Bromus kordeaceus, Trifolium arvense, Hypochoeris radicata, &c. (vi.) The Animal Factor. The animal factor, except as regards insects and their pollinating-power and birds as seed-carriers, was a minus quantity in primitive New Zealand. Human settlement has changed all that. The matter, however, needs no discussion here; it has been already dealt with to some extent, and receives further notice in more than one place. At the present time it is one of the most important factors in retarding dune-reclamation. (vii.) Fire. Fire is dealt with in Part 11, and its effects for evil need no emphasizing. It too was a factor not affecting the primitive vegetation. (c.) THE MOST CHARACTERISTIC PLANTS, THEIR OROWTH-FORMS AND ADAPTATIONS. (i.) General. \\ ere it not for the, instability of the dunes caused by the drifting sand, no special " adaptations " would be required by their plants other than those demanded by excessive wind, dry soil, strong insolation, &c, and which are possessed by xerophytic plants of various other formations. The dune-plants proper — i.e., those which not only federate but benefit by a partial sand-burial - are almost as highly specialized for their mode of life as lianes, which in some respect they resemble in their greal length of stem. This latter enables them to spread over wide areas, and to increase rapidly by vegetative means, a great advantage under conditions so antagonistic to the welfare of seedlings. But it is the special power of the shoot-apex to grow upwards as it is buried which enables this growth-form to cope with the constant increase of sand. This peculiarity possessed by duneplants of all regions has already been mentioned under the term " sand-binding," and is present to a