General.

These problems may be thus stated: How are we to account for the survival, in an exceedingly limited area, of a very special and peculiar formation, and in very limited numbers, of a plant which is obviously adapted to a climate very different from that of the present time, which reproduces itself only by seed, not vegetatively, and that only in a very sparing manner, and which apparently can exist only upon a kind of soil occurring only in limited areas separated from one another by great distances?

Apart from geological history several considerations may here be given as bearing upon the main problems.

Reproduction and Distribution of Seed.—The achene, on dropping off, no doubt falls into the soil and is moved by the wind, as the surface of the debris is quite unstable, most of the plants being actually buried in it above the rootstock. It is remarkable that none of the plants of this association is a “traveller.” The seed of all is presumably distributed in the same way—by the action of the wind in shifting the soil; none of them is provided with a pappus or coma; no composite plant except Raoulia australis enters into the unit. Epilobium gracilipes and Senecio Monroi var. dentatus, which occur on the steep slopes and rocks above the basin and have seeds specially adapted for carriage to a distance by the wind, are absent altogether from the flatter portions of the area.

Instability of Soil.—The wind is always bringing fresh debris into the basin, and is always stirring and shifting all that part of the surface which is entirely or nearly bare. As the rocks are now always rapidly crumbling, and no doubt have been in the same state for a very long period of time, it follows that they must formerly have been much larger than they are now; therefore they must formerly have set free annually a much larger amount of material, and therefore the superficial area of unstable debris must formerly have been much greater. But in recent times the area of bare debris could never have been really extensive, as the accumulation of it would hardly be possible under present conditions except within the enclosed space of the basin. However, in some much older age it may be imagined that a much greater area lying eastward of the small basin might during a period of steppe climate or drought become a semi-desert, mainly of this debris, supporting a calciphile and xerophytic flora, in open formation, of such individuals and in such disposition as we now see within the enclosed and protected area only.

Struggle for Life.—As Warming (1909, p. 256) observes of fell-field in general, the typical xerophytic plants are so thinly distributed that they do not interfere with one another nor compete with one another. It is so here, and it is so upon the steep shingle-slopes of the dry eastern mountains of the neighbourhood. Ranunculus Haastii, for instance, is exactly like R. paucifolius in this respect. Only a certain small number of plants grow within a given space, when, so far as one can see, an infinitely greater number might grow there without in the least inconveniencing their neighbours.

Thus Ranunculus paucifolius has not been threatened with extinction in this manner. It seems, however, to have had to face two other dangers in recent times. On the one hand, if the surface upon which it grows were for any cause to become still more unstable, and the wind to act