In this connection I might allude to the many plants which are more or less viscid. This also is in most cases a provision to preclude creeping insects from access to the flowers.
There are various other kinds of hairs to which I might refer—glandular hairs, secretive hairs, absorbing hairs, etc. It is marvellous how beautifully the form and structure of leaves is adapted to the habits and requirements of the plants, but I must not enlarge further on this interesting subject.
The time indeed will no doubt come when we shall be able to explain every difference of form and structure, almost infinite as these differences are.
INFLUENCE OF SOIL
The character of the vegetation is of course greatly influenced by that of the soil. In this respect granitic and calcareous regions offer perhaps the best marked contrast.
There are in Switzerland two kinds of Rhododendrons, very similar in their flowers, but contrasted in their leaves: Rhododendron hirsutum having them hairy at the edges as the name indicates; while in R. ferrugineum they are rolled, but not hairy, at the edges, and become ferrugineous on the lower side. This species occurs in the granitic regions, where R. hirsutum does not grow.
The Yarrows (Achillea) afford us a similar case. Achillea atrata and A. moschata will live either on calcareous or granitic soil, but in a district where both occur, A. atrata grows so much the more vigorously of the two if the soil is calcareous that it soon exterminates A. moschata; while in granite districts, on the contrary, A. moschata is victorious and A. atrata disappears.
Every keen sportsman will admit that a varied "bag" has a special charm, and the botanist in a summer's walk may see at least a hundred plants in flower, all with either the interest of novelty, or the charm of an old friend.
ON SEEDLINGS
In many cases the Seedlings afford us an interesting insight into the former condition of the plant. Thus the leaves of the Furze are reduced to thorns; but those of the Seedling are herbaceous and trifoliate like those of the Herb Genet and other allied species, subsequent ones gradually passing into spines. This is evidence that the ancestors of the Furze bore leaves.