170 THE BOOK OF NATURE STUDY 



growth of the oak is easily traced ; in Fig. 49, that of the ash, 

 only one year's growth is visible. 



All the buds on a twig do not necessarily develop into branches. 

 Many remain dormant, ready to develop if through injury any 

 branch dies off. Very commonly the buds at the base of a shoot 

 do not develop for want of nourishment which has been snatched 

 from them by the buds above. Such buds may remain dormant 

 for years, and then develop if a branch above has been pruned 

 or broken off by wind, or the weight of snow. The thinning of 

 a wood may supply the necessary stimulus, through the greater 

 light and air now available. This accounts for the fact that 

 beeches, elms, and limes often have bushy outgrowths on the 

 lower parts of stems which had been naked. The cutting off 

 the upper parts of a tree will, for the same reason, stimulate the 

 outgrowth of suckers from the base of the stem, as in the elm, ash, 

 oak, etc. The bud of the plane should be examined. At first 

 sight, whilst the leaves are on the tree, it appears to have none ; 

 but if the leaf is gently pulled off, the bud will be found nestling 

 in the hollowed-out petiole, which covers it completely. 



The angle which the branches make with the shoot bearing 

 them should be observed, as the mode of branching is character- 

 istic of the tree. This depends to some extent on the insertion 

 of the buds. It is easy to see in winter that some buds are 

 almost at right angles to the shoot, others again are almost erect, 

 practically parallel to the shoot, and in some trees the buds may 

 be inclined at an angle of 45. It is thought that on the whole 

 the upper and stronger shoots make a more acute angle with 

 the parent stem than the lower ones. It will be found that the 

 branches of a tree do not always maintain the same inclination 

 to the parent shoot. To realise how they may differ, trees may 

 be drawn in winter, when the branching is clearly seen. 



Trees and shrubs are specially protected in the winter by 

 bark, which is formed on their trunks and branches. It arises in 

 this way. The outer skin of the stems of most trees and shrubs 

 cannot grow as fast as the underlying tissues, and therefore 

 cracks. Through these cracks water and insects might find 

 their way, but a layer of cork forms beneath the outer skin and 

 gradually spreads all round the stem ; it may be recognised by 



