LEAF-BUDS Al^D BRANCHES. 113 



buds, a woody plant is made to assume a bushy appearance, and thus 

 pollard trees are produced. Pruning has the effect of checking the 

 growth of terminal buds, and of causing lateral ones to push forth. 

 The peculiar bird-nest appearance often presented by the branches of 

 the common Birch depends on an arrestment in the terminal buds, a 

 shortening of the internodes, and a consequent clustering or fascicula- 

 tion of the twigs. In some plants there is a natural arrestment of the 

 main axis after a certain time, giving rise to peculiar shortened stems. 

 Thus the crown of the root (p. 46) is a stem of this nature, forming 

 buds and roots. Such is also the case in the stem of Cyclamen, 

 Testudinaria Elephantipes, and in the tuber of the potato. The pro- 

 duction of lateral in place of terminal buds sometimes gives the stem 

 a remarkable zigzag aspect. 



In many plants with a shortened axis, the lateral buds produce 

 long branches. Thus the flcu/ellum (Jlagelhim, a whip or twig), or 

 runner of the Strawberry and Eanunculus, is an elongated branch, 

 developing buds as it runs along the ground ; the propagulum (pro- 

 pago, a shoot), or offset, is a short thick branch produced laterally in 

 fleshy plants from a shortened axis, and developing a bud at its ex- 

 tremity, which is capable of 

 living when detached, as in 

 Houseleek. Fig. 223 repre- 

 sents a strawberry plant, in 

 which a' is the primary axis, 

 ending ia a cluster of green 

 leaves, r, and some rudi- 

 mentary leaves, /, and not 

 elongating ;_ from the axil of 

 one of the leaves proceeds a 

 branch or runner, a", with a 

 rudimentary leaf,/, about the Fig. 223. 



middle, and another cluster 



of leaves, /" and r, forming a young plant with roots ; from this a 

 third axis comes ofi", a", and so on. In many instances the runner 

 decays, and the young plant assumes an independent existence. 

 Gardeners imitate this in the propagation of plants by the process 

 of layering, which consists in bending a twig, fixing the central part 

 of it into the ground, and, after the production of adventitious roots, 

 cutting off its connection with the parent. 



When the stem creeps along the surface of the ground, as in 

 the Ehizome (flg. 107), or completely under ground, as in the Soboles 



Fig. 223. Flagellum or Runner of the Strawbeiry. a'. One axis wlioh has produced a 

 cluster of leaves, the upper, r, green, the lower, /, rudimentary. Prom the axil ot one of the 

 latter a second axis, a", arises, hearing about the middle a rudimentary leaf, /', and a cluster 

 of leaves, r, partly green and partly rudimentary, /", at its extremity. Prom the axil of one 

 of the leaves of this cluster a third axis, a, proceeds. 



I 



