Creeping stems.—Instead of climbing, many stems find that the best method of spreading out their leaves is to creep along or under the ground, and give off leaves and roots at intervals. Not only does this device prevent the leaves of one node from interfering with the light and air supply of those of the next, but the plant is continually coming in contact with a fresh lot of soil. The ground ivy is an instructive example of this method of growth. The stem creeps along the ground, and at every node it gives off a pair of leaves which grow upwards, and a tuft of roots which grow down into the ground.
Fig. 50.—Runner of Strawberry. (× ⅓.)
The runner of the strawberry ([Fig. 50]) appears at the first glance to grow in a similar manner. As a matter of fact, however, the apparent stem is a branch arising in the axil of one of the leaves of the last node. The branch runs along the ground and gives rise to a new shoot, and from this another branch, springing from the axil of a leaf, forms another runner. The same branch does not run on from shoot to shoot.
The stolon of the couch grass ([Fig. 51]) is somewhat similar. The erect stem of the plant is divided, as usual, into nodes or knots (from which the narrow, sheathing leaves arise) and internodes. Branches (stolons) spring in the axils of the lower leaves, turn downwards, and run on underneath the soil, taking root again at some distance from the parent plant.
Fig. 51.—Stolon of Couch Grass. (× ⅙.)