VEGETATIVE INCREASE 53 
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 char- 
acteristic 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 in- 
dividual. 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-dis- 
persal 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 
