100 THE STEM. 



nal one is regularly suppressed, and the lateral grow, when the 

 stem annually becomes forked, as happens in the Lilac (Fig. 129). 



151. The undeveloped buds do not necessarily perish, but are 

 ready to be called into action in case the others are checked. 

 When the terminal buds are destroyed, some of the lateral, that 

 would else remain dormant, develope in their stead, incited by the 

 abundance of nourishment, which the former would have monop- 

 olized. In this manner our trees are soon reclothed with verdure, 

 after their tender foliage and branches have been killed by a late 

 vernal frost, or other injury. The buds may remain latent even 

 for years, and become covered with wood. The trunk of a tree, 

 therefore, always contains an immense number ; some of which, 

 after a long period, may force their way through the wood to the 

 surface, and break forth into branches ; especially when the tree is 

 pollarded, or its leading branches injured. 



152. Adventitious Buds, But many such branches have an abnor- 

 mal origin, from irregular or adventitious buds, like those pro- 

 duced by roots under similar circumstances (125). Such buds are 

 still more readily produced on woody stems, when surcharged 

 with sap, as we constantly observe on pollard Willows and Lorn- 

 bardy Poplars. Indeed, in several instances, buds are known to 

 arise even from the surface or margins of leaves, as in Bryo- 

 phyllum, which derives its name from this unusual circumstance ; 

 and the gardener produces them from root-cuttings or leaf-cuttings 

 of certain plants, which he propagates in this way. Adventitious 

 buds originate in the parenchyma, some cells of which are incited 

 to take an independent development. In trees, they form on the 

 surface of the wood, at the ends of the lines of the silver-grain 

 (medullary rays, 191, 196). They are especially liable to spring 

 from the new cellular tissue that forms at the growing season 

 between the wood and bark when the trunk is wounded or cut off. 

 Thus the predestined symmetry of the branches is obscured or 

 interfered with in two distinct ways ; first, by the failure of a part 

 of the regular buds to develope ; and secondly, by the irregular or 

 casual development of buds from other parts than the axils of the 

 leaves: to which we may add, that great numbers of branches 

 perish and fall away after they have begun to grow or have at- 

 tained considerable size. There is still another source of irregu- 

 larity, namely, in the production of 



153. Accessory Buds, These are, as it were, multiplications of 



