96 PHYLLOTAXT. [CH. VII 



of some leaf-scars are seen withered undeveloped axillary 

 buds. 



At irregular intervals on the branch are seen finely 

 wrinkled places, about J inch in length ; these are made 

 by the scars of scale-leaves ; under a lens the scars can be 

 seen to resemble those of the foliage-leaves, except that 

 they are relatively wider and shorter, and that the scars 

 of the bundles are less evident, or indeed not to be seen. 

 Each wrinkled place represents the spot where a terminal 

 bud once existed, we have therefore evidence of how much 

 the branch grew from year to year. Thus we get by 

 different means the same sort of evidence of yearly 

 growth as is yielded by the annual rings in wood. 



The horse-chestnut not only serves as an illustration 

 of foliage- and scale-leaves, it also serves to demonstrate 

 one of the common modes in which foliage-leaves are 

 arranged on the branch. When the leaves grow opposite 

 to each other in a plane at right angles to that in which 

 the pairs of leaves above and below are developed, the 

 arrangement is known as decussate. This decussate 

 arrangement is common, but it is by no means the only 

 one, great variety exists in this matter, and a special name, 

 phyllotaxy, has been given to this department of morpho- 

 logy. In many plants the leaves are alternate; thus 

 one leaf will be on the north side, then at the next node 

 the leaf will be southerly, then north again one stage 

 higher. In this case the leaves are arranged in two 

 vertical rows : in the horse-chestnut there are four vertical 

 rows, while in other plants a larger number exists. In the 

 groundsel for instance the leaves are in five vertical rows. 



