The migrations of plants are effected mainly during the seed stage, these tiny, tightly packed portmanteaux being much better fitted for travel than the bulky and fragile organisms to which they give rise. But before we consider the adventures of seeds it must be pointed out that a considerable, if slow, migration of plants takes place by mere vegetative growth. The stems of many species are not erect, but prostrate; creeping upon or below the ground, they may in time cause a plant to spread far beyond its place of origin. A whole field, or for that matter a whole hillside, of Bracken (_Pteris Aquilina_) may quite possibly have originated from a single wind-borne spore. Among Sedges and Grasses this mode of growth is common--as we know to our cost in the case of the Couch-grass (_Triticum repens_)--and it is found in varying form in many kinds of plants, as in the suckers of trees, the offsets of bulbs, the runners of the Strawberry (_Fragaria_); it is especially characteristic of marsh and water plants. Its effect is to produce large colonies, such as the great beds of Reeds (_Phragmites_) or Reed-mace (_Typha_) which fringe our lakes, the groves of Bent (_Ammophila_) on sand dunes, and the beds of Anemones (_A. nemorosa_) or Broad-leaved Garlic (_Allium ursinum_) of our spring woods. In all these cases the whole colony may be the result of the continued growth of a single individual. It should be noted, however, that such migration is possible only so far as favourable soil conditions extend. A slight barrier--a streamlet, a patch of ground too wet or too dry, will arrest further progress, and the plant must fall back on seed-dispersal in order to conquer further territory. A vegetative device which, so far as its method and value in dispersal are concerned, approaches those of seeds, is found in the bulbils with which some plants are furnished. These are small buds--congested shoots--borne on stems, or on leaves as in the Lady’s Smock (_Cardamine pratensis_), or among the [Illustration: FIG. 7.--CORAL ROOT (DENTARIA BULBIFERA). _a_, Upper half of shoot, 1/2; _b_, creeping stem, 1/2; _c_, bulbil, 2/1.] flowers as in many Leeks (_Allium spp._). These usually fall from the parent when mature, and being comparatively small and possessed of considerable vitality, they may achieve a considerable dispersal before they send out roots and fasten themselves to the soil. An example is figured (Fig. 7). In this plant (_Dentaria bulbifera_, the Coral Root, a rather rare native of England) the bulbils resemble not the smooth flower-stems of which they are axillary branches, but the curiously knobby underground stems from which the leaves and flowering shoots arise. Since seeds themselves possess, as already stated, no power of locomotion, they have to rely on external agents for their dispersal. These may in general be summed up as (1) Action of the parent plant, (2) water, (3) wind, (4) animals.