ORGANS OF NUTRITION. 



11 



parts of tlic plant ; these will be referred to hereafter, under the 

 heads of the organs of which they are respectively modifications. 



Kinds ov Stems. — We have seen that the stem, when first de- 

 veloped, always takes a diametrically opposite direction to that 

 of the root. In many instances this direction is continued more 

 or less throughout its life. In other plants, however, the termi- 

 nal bud cither acquires an irregular direction, and the stem runs 

 along, or remains under, the surface of the ground ; or it jjcrishes 

 altogether at a very early period, and an axillary branch will 

 take its place, and this also, by devcloi)ing laterally, will like- 

 Avise continue near the surface of the ground, or burrow beneath 

 it. From these peculiarities in the direction and growth of 

 stems and branches, we have a number of modifications which 

 we have now to describe. These are best treated of under two 

 heads, namely, those which are aerial, and those wliich arc 

 subterranean. Wc can, however, by no means draw a distinct 

 line between the modifications of stem which these two divisions 

 respectively contain, as certain forms occasionally pass from one 

 into the other, thus being both subteiTanean and aerial at diffe- 

 rent points, or at different periods. 



1. Aerial Modifications of the Stem. — Of these we shall describe 

 the runner, the offset, the stolon, the sucker, and the rhizome. 



a. The Runner. (Fig. 211.) — This is an elongated slender pro- 

 strate branch, sent off from the base of the stem, and giving off 

 at its extremity roots and leaves ; thus producing a new plant, 



Fig. 211. A portion of the common Strawberry plant, a'. An axis prodm-- 

 ing a tuft of leaves, r, at its extremity, from the axil 6f one of wliich 

 another axis or runner, o", arises, bearing a rudimentary leaf, /, near the 

 piiddle, and a cluster of leaves, r, at its end. a. A third axis produced 

 In a similar manner to the former. 



which extends itself in a similar manner. It is well seen in the 

 common Strawberry and Potcntilla. The runner is sometimes 

 known under the name of tlie flagcllum, hence such branches 

 are tcrnn^dJlageUiforjn. 



