SEASONAL CHANGES 



169 



The base of the leaf -stalk of a fallen leaf is yellow, owing to the 

 development of cork. As soon as the cork is formed, water, and the 

 substances it contains in solution, can- 

 not get from the stem to the leaf. Not 

 getting nourishment, and not being able 

 to make starch, owing to the partial de- 

 composition of the chlorophyll, the leaf 

 is starved and falls, leaving a scar just 

 beneath the bud formed in its axils. 

 These scars are very large and horse- 

 shoe shaped in the horse-chestnut, 

 showing plainly the position of the 

 wood bundles which conducted water 

 from the stem to the leaf. They may 

 also be distinctly seen in the ash, but 

 are less conspicuous in the beech. 



In the winter the buds are protected 

 by bud-scales, which prevent the damp 

 and cold reaching the young foliage 

 and floral-leaves within. The difference 

 in the position of buds, and therefore 

 of branches, may be studied in the 

 oak and in the ash. In the former 

 case the buds are much more crowded 

 at the apex of the twig, and they are 

 alternate, not opposite, as in the ash. 

 The twig of an ash terminates in 

 a leaf-bud, and just below the apex 

 there are two axillary buds, one on each side of the apical one. 

 The branching of this tree is far simpler than that of the 

 oak, whose branches are more crowded. The ash often has 

 remarkably long shoots, and the year's growth of a twig may 

 reach a considerable length. In the oak the internodes are 

 generally far shorter, the nodes consequently much nearer each 

 other, and the branches crowded. The length of each year's 

 growth may be easily seen in the winter, when the leaves have 

 fallen, for the scars left by the scales of the last year's apical bud 

 form a ring round the stem of the twig. In Fig. 48, two years' 



FIG. 49. One-year-old twig of 

 Ash. #, Node ; int, internode ; 

 s, scars left by last year's 

 leaves ; ss, scars left by last 

 year's bud- scales, showing the 

 limit of the year's growth. 



