WINTER BUDS, SHOOTS, ETC. II 



This is the growing cylindrical layer of the shoot which lies 

 between the bark and wood throughout the extent of the shoot 

 and in fact the entire tree. It is the cambium. 



22, Annual rings in woody stems, If we now cut across a 

 ehoot of the ash which is several years old, we shall note, as 

 shown in fig. 5, that there are successive rings which have a 

 similar appearance to the woody ring in the one-year-old stem. 

 This can well be seen without any magnification. The larger 

 size of the woody ducts which are developed each spring, and 

 the preponderance of the fibres at the close of each season's 

 growth, mark well the growth in diameter which takes place 

 each year. 



For further details consult Chapter XI, and also the author's 

 larger " Elementary Botany." 



23. Phyilotaxy, or arrangement of leaves. In examining 

 buds on the winter shoots of woody plants, we cannot fail to 

 be impressed with some peculiarities in the arrangement of these 

 members on the stem of the plant. 



In the horse-chestnut, as we have already observed, the leaves 

 are in pairs, each one of the pair standing opposite its partner, 

 while the pair just below or above stand across the stem at right 

 angles to the position of the former pair. In other cases (the 

 common bed straw) the leaves are in whorls, that is, several 

 ctand at the same level on the axis, distributed around the 

 Ltem. By far the larger number of plants have their leaves 

 arranged alternately. A simple example of alternate leaves is 

 presented by the elm, where the leaves stand successively on 

 alternate sides of the stem, so that the distance from one leaf 

 to the next, as one would measure around the stem, is exactly 

 one half the distance around the stem. This arrangement is ^, 

 or the angle of divergence of one leaf from the next is . In 

 the case of the sedges the angle of divergence is less, that is . 



By far the larger number of those plants which have the 

 alternate arrangement have the leaves set at an angle of diver- 

 gence represented by the fraction f . 



