I 3 2 ROUND THE YEAR 



The protection of leaf-buds is effected in various 

 ways. The bud-scales are sometimes downy, as in 

 buds of the Willow ; sometimes they pour forth a 

 sticky substance, made of resin or gum, especially at 

 the time when the bud is just ready to open. Such 

 secretions are found in the buds of the Horse-Chest- 

 nut and the Black Poplar. Hairs protect the bud 

 from both cold and wet, chiefly by enclosing air, 

 which cannot easily be dislodged from very narrow 

 spaces. Imprisoned air is a very bad conductor of 

 heat, and it does not allow water to penetrate. 

 Even when the bud-scales are not downy, the thin 

 layers of air between them are a great protection. 

 Sometimes the bud-scales are excavated by broad 

 and very thin air-spaces. Many buds, especially of 

 herbaceous plants, are buried beneath the ground. 



But for disturbing circumstances, which are, how- 

 ever, inevitable in the case of trees and shrubs, every 

 leaf would develop a bud in its axil, that is, in the 

 angle between it and the main stem. It is easy to 

 see that the shoots would become terribly crowded if 

 every leaf produced its bud, and every bud formed 

 a shoot. But poorly illuminated leaves often produce 

 no buds in their axils, or the buds fail to expand. 

 At the tips of the branches, on the other hand, where 

 the light is profuse, large buds, developing strong 

 shoots, will appear. Hence the branching is most 

 vigorous in an upward and outward direction. Many 

 variations are to be observed, and these lead to 

 variations in the mode of branching, and therefore in 

 the form of the full-grown tree. If the terminal bud 

 is larger than any of the lateral ones, and expands 



