We have already referred to several species which are essentially flowers of the woods, but even these are not distributed evenly in wooded districts; for while some seem to be more universally scattered throughout our wooded parts, others show a decided partiality to particular soils, being found exclusively, or almost so, either in sandy woods, clayey woods, or woods in limestone districts, &c. In fact, the nature of the soil is such an important factor in determining plant distribution that we naturally associate many species with the particular rock strata on which we almost invariably find them. So intimately is the distribution of plants connected with that of the geological strata that when, in the course of a day's ramble, we find a more or less sudden change in the nature of the flora, we may be almost sure that there is a corresponding change in the nature of the rocks or soil over which we have strayed; and the young botanist will find much to interest him in the study of this relation between vegetable life and geological structure. Of course we do not mean that the botanist must necessarily be also a geologist, but that he should, at least, be always ready to observe the nature of the habitats of the flowers he finds, noting particularly the kind of soil on which they grow. [Illustration: _Plate VIII._ FLOWERS OF CHALKY SOILS. 1. Red Valerian. 2. Narrow-leaved Flax. 3. Tufted Horse-shoe Vetch. 4. Spiked Speedwell. 5. Pasque Flower. 6. Bee Orchis. 7. Yellow Oat Grass.] Chalky districts are notably attractive to the lover of flowers; for, not only do they yield a number of species that are almost essentially the offspring of calcareous soils, but also produce other blossoms, often in rich profusion, that are less restricted in their habitats. [Illustration: THE ROCK ROSE.] In the present chapter we shall note the principal flowers that grow principally or entirely in calcareous districts, the first being the Pasque Flower (_Anemone Pulsatilla_--order _Ranunculaceæ_), rare, it is true, but too beautiful to be omitted from our selection. This flower, shown on Plate VIII, Fig. 5, may be seen on some chalky hills during May and June. It is of a silky nature, and the lovely purple blossoms often reach a diameter of an inch and a half. The leaves are doubly or trebly pinnate, with very narrow segments which increase in length after the flowers have faded. The bracts, which are some distance below the flower, have also linear segments; and the flowers droop while still in the bud, but the peduncle becomes erect as they expand. The stamens are yellow, and the fruits are provided with feathered hairs.