If we view the vegetation as a whole, we may be tempted to enquire first as to its origin and history. We know that plants have existed on the earth for millions of years, but that the plants of past ages were different from those of the present, just as those of the present will ultimately give place to other forms as yet undreamed of: that the vegetation on which we feast our eyes is, in fact, but the momentary expression of a never-ceasing process of life and change. This is the point of view of the geologist, to whom
The hills are shadows, and they flow
From form to form, and nothing stands;
They melt like mist, the solid lands,
Like clouds they shape themselves and go.
Pursuing this line of enquiry, we may endeavour to trace the descent through the ages of our present plants from bygone types; and coming at length to the still remote time—as measured by human standards—when the plants which now grow appeared on the Earth’s surface, we may try, from a study of their present distribution and of the distribution of their remains in regions where they are no longer found living, to determine their area of origin, and to trace the date and course of the migrations by which they reached our country. In the case of the British Isles, geological considerations play a leading part in such investigations, these islands being but outlying hummocks of a great continental area, at times joined to the main land-mass by a slight upward movement of the Earth’s crust, and anon cut off from it by a movement of depression. In this connection also we may be led to investigate the means by which plants spread, and especially their capacity for crossing barriers of the various kinds indicated in our brief study of deserts in the previous pages—the serious barriers offered by water-channels, or others equally difficult to negotiate produced by areas of uncongenial soil, by mountain ranges, or by forests. This will involve especially a study of seeds and the interesting phenomena of seed-dispersal.
Again, the most popular branch of botanical study in England is Floristic Botany, which traces the distribution within our area of the various species composing its flora; and with it is necessarily associated a study of the plants themselves so far as the characters are concerned, by which they may be distinguished from each other. This last is the province of Descriptive Botany. The study of local distribution, if conducted intelligently, will greatly assist in solving problems relating to the migrations and routes by which the existing flora reached its habitats.
Once more, we have already from Farleton Fell observed that plants do not grow higgledy-piggledy over the country, but are arranged in more or less definite societies depending on similarity of climate, soil, and other external conditions. Studied from this point of view, the flora resolves itself into a series of communities, each requiring a certain set of conditions for its continued welfare. The study of these inter-relations between plants and their environment, and of the types of vegetation resulting from the grouping together of plants requiring similar conditions, is the province of Ecological Botany.
Again, the morphologist deals with the forms of the organs of plants, and the changes which these undergo in different plants, while the anatomist investigates their minuter structure.
Physiological Botany deals with the life processes of plants, and the way in which they feed and grow and move. It has a very important bearing on the distribution and grouping of plants, since this is largely governed by their food-supply and by the need of surroundings which allow them to carry on their life processes with success.
It will be seen that there are many lines of enquiry open to the student of botany. In the following pages no more can be attempted than the preliminary study of some of the more familiar phenomena of plant life as it presents itself to the holiday-maker on the hills and woods and shores of our own land.
CHAPTER II
PLANT ASSOCIATIONS
“It is perhaps also proper to take into account the situation in which each plant naturally grows or does not grow. For this is an important distinction, and specially characteristic of plants, because they are united to the ground and not free from it like animals.”—Theophrastus: Enquiry into Plants, I. iv.