LEAVES 105 



Then, also, the arrangement of leaves upon the 

 stem {pliyllotaxis) varies much. If we take a spraj' 

 of beech uc shall find that its buds are jjlaced 

 alternately on either side of the stem, so that the 

 third l)ud is exact!)' IjcIow the first, and the second 

 bud is in a line w ith the fourth, and so on. This 

 is also the plan of the elm, hazel, lime, hf)rnbeam, 

 and man)' other trees. In the alder and white- 

 beam the buds occur in three rows, and in some of 

 the willows in .series of eii^^ht. 



The leaves of the horse-chestnut arc borne in 

 pairs on alternate sides of the stem, and this j^lan 

 is common to a number of plants, especiall)' those 

 of the type of the dead nettle and speedwell. 



OuJte a distinct arrangement is that to be found 

 in the woodruff and bedstraws, where the lea\es 

 are placed in a ring (a whorl) at regular intervals on 

 the stem. 



The botanical student should carefull)- observe 

 the differing methods of leaf arrangement, since, 

 as branches are developed from buds, the var)'ing 

 order in their jjosition must naturall)- modif)' the 

 general aspect of a tree, and has also much 

 physiological imi)ortancc. W'c shall find that 



