TENDRIL OE CIEEUS. 121 



with the view of enabling the plant to climb. In the Vine the tendrils 

 are looked upon as the terminations of separate axes, or as transformed 

 terminal buds, and are sometimes called sarmenta. In the Vine there 

 are no young buds seen in the angle between the stem and leaves, nor 

 between the stem and tendrils ; and the latter are not axillary. Fig. 

 239 represents the branch of a Vine, in which a is the primary or first 

 formed axis, ending in v', a tendril or altered terminal bud, and having 

 a leaf, /', on one side. Between this leaf and the tendril, which repre- 

 sents the axis, a leaf-bud was formed at an early date, producing the 

 secondary axis, or branch, o", ending in a tendril, v", with a lateral leaf, 

 /", from which a tertiary axis or branch, a", was developed, ending in a 

 tendril v", and so on. The tendrils of Ampelopsis Veitchii are termi- 

 nated by discs which secrete a sticky matter, by means of which they 

 adhere to walls, etc. The tendrils, like those of the Vine, are modi- 

 fications of the axis. 



Tendrils twist in a spiral manner, and enable the plants to rise 

 into the air by twining round other plants. The direction of the spiral 

 frequently differs from that of the climbing stem which produces 

 the tendril. In the Vine, the lower part of the stem is strong, and 

 needs no additional support ; the tendrils therefore occur only in the 

 upper part, where the branches are soft, and require aid to enable 

 them to support the clusters of fruit. In the vanUle plant (Vanilla 

 aromatica) the tendrils are produced opposite the leaves, until the 

 plant gains the top of the trees by which it is supported ; the upper 

 tendrils being then developed as leaves. The midrib is sometimes 

 prolonged in a cup-like or funnel-shaped form ; this is occasionally 

 seen in the common cabbage, and seems to depend on the vascular 

 bundles of the midrib spreading out at their extremity in a radiating 

 manner, and becoming covered with parenchyma in such a way as to 

 form a hollow cavity in the centre. 



Special Functions of Leaves. 



Leaves expose the fluids of plants to the influence of air and 

 light. The fluids so exposed are elaborated, and thus fitted for the 

 formation of the various vegetable tissues and secretions. For the 

 proper performance of this function the structure of the leaves and 

 their arrangement on the stem and branches, renders' them well 

 adapted. A plant, if constantly stripped of its leaves, is destroyed, 

 from non-development of tissue and absence of secretions. On this 

 principle, weeds, with creeping stems and vigorous roots, which are 

 with difficulty eradicated, may be killed. The elaboration of fluids 

 in the leaves necessarily implies interchange of their constituents with 

 those of the surrounding atmosphere ; hence two processes are inevi- 

 table — a passing inwards into the leaf of the atmospheric elements 



