Fig. 254. A colony of clotbur.
When an area is newly cleared, many plants rush for it. Quickly it is covered with ambitious growths,—pokeweeds, fireweeds, thistles, briars, nettles. Often each plant occupies large places alone, making clumps or patches. These patches are plant colonies,—made up mostly of one species or kind ([Fig. 254]). But as the struggle tightens, other plants insinuate themselves into the colony and it is broken up; a mixed population results. Sometimes these colonies are broken up by the shade of trees and tall bushes which have come up near them, for all neglected areas, in this part of the world, tend to return to forest if they are not mown, pastured or burned. Mown and pastured areas run into grass, for the grass withstands the cutting and grazing. In burned areas the struggle begins anew when the fire has passed.
Plant societies are easy to study for the school. The study of them appeals to the desire for exploration and adventure, and adds zest to the excursion. Go to a swale, swamp, roadside, forest, weedy field, or other place, and ask the pupil to note: (1) that the flora of the place is unlike that of places with different physical features; (2) that these particular plants grow together because they can all survive under similar conditions; (3) what these conditions are,—whether sun, shade, dry soil, wet soil, sand, clay, rock; (4) what particular plant is most abundant or gives character to the society.
Fig. 255. Two plant societies,—the close-bitten sward and the rushy pond.
Study one society thoroughly. Make lists of the kinds of plants and of the relative numbers of each. If the names of the plants are not known, call them by numbers; make dried specimens of them for reference. When another society is visited, repeat these observations, and compare one society with another.
Fig. 256. The edge of the road. Trees and bushes crowd the drive-way, and a ribbon of grass and weeds has pushed itself to the very margin.