112 . LEAF-BUDS AND BKANCHES. 



extremities and are accumhent or opposite (fig. 222 k), or are folded 

 inwards by their margin, and become induplicaie (fig. 222 Z) ; or a 

 conduplicate leaf covers another similarly folded, which in turn covers 

 a third, and thus the vernation is equitant (riding), as in Privet 

 (fig. 222 m) ; or conduplicate leaves are placed so that the half 

 of the one covers the half of another, and thus they become half- 

 - equitant or ohvolute, as in Sage (fig. 222 n). The scales of a bud 

 sometimes exhibit one kind of vernation, and the leaves another (fig. 

 221). The same modes of arrangement occur in the flower-buds, as 

 wHl be afterwards shown. 



Leaf-buds, as has been stated, are either terminal or lateral. By 

 the production of the former (fig. 219 ht), stems increase in length, 

 while the latter (fig. 219 ha, ha, ha) give rise to branches, and 

 add to the diameter of the stem. The terminal leaf-bud, after pro- 

 ducing leaves, sometimes dies at the end of one season, and the whole 

 plant, as in annuals, perishes ; or part of the axis is persistent, and 

 remains for two or more years, each of the leaves before its decay 

 producing a leaf-bud in its axil. This leaf-bud continues the growth 

 in spring. 



In some trees of warm climates, as Oycas, Papaw-tree, Palms, 

 and Tree ferns, the production of terminal buds is well seen. In these 

 plants the elongation of the stem is generally regular and uniform, so 

 that the age of the plant may be estimated by its height. Such stems 

 (often endogenous) may thus be considered as formed by a series of 

 terminal buds, placed one over the other. From this mode of growth 

 they do not attain a great diameter (fig. 134, 1). In other trees, 

 especially Exogens, besides the terminal bud there are also lateral 

 ones. These, by their development, give rise to branches (rami), from 

 which others, called branehlets or twigs (ramuli) arise. Such buds 

 being always produced in the axil of leaves are of course arranged in 

 a manner similar to the leaves. By the continual production of lateral 

 leaf-buds, the stem of exogenous plants acquires a great diameter. 



Although provision is thus made for the regular formation of 

 leaf-buds, there are often great irregularities in consequence of many 

 being abortive, or remaining in a dormant state; Such buds are 

 called latent, and are capable of being developed in cases where the 

 terminal bud, or any of the branches, have been injured or destroyed. 

 In some instances, as in Firs, the latent buds follow a regular system 

 of alternation ; and in plants with opposite leaves, it frequently hap- 

 pens that the bud in the axil of one of the leaves only is developed, 

 and the different buds so produced are situated alternately on opposite 

 sides of the stem. 



When the terminal bud is injured or arrested in its growth, the 

 elongation of the main axis stops, and the lateral branches often 

 acquire increased activity. By continually cutting off the terminal 



