FOLIAGE. 145 



By a close examination with the lens, it is generally 

 easy to find whether the rain passes down the stem or 

 not. If it passes down dust particles accumulate towards 

 the base of the leaves and thus explain the ordinary 

 course of the water. Channelled or grooved leaf-stalks, 

 as well as broad and permanent stipules, generally act 

 as rain directors. It is also very easy to find out by 

 experiment how the water travels. 



A very neat arrangement to carry away rain is seen 

 in almost all the grasses. The leaf consists of two parts 

 of which the lower is a tube or sheath enclosing a white, 

 delicate part of the stem, whilst the rest of the leaf is 

 flat and green and is used for the ordinary work of 

 assimilation. At the junction of these two parts there 

 is generally a small white scale forming a distinct rim 

 round the stem. Water coming down the leaf is turned 

 aside by this white scale, or ligule^ and cannot enter into 

 the tube or sheath, where it might bring bacteria and 

 cause decay in the soft stem tissue. But some British 

 grasses, such as Melica, have no ligule and in this form 

 the leaves droop over the stem which is also inclined in 

 such a way that rain could not enter in any case. 



Storms are fortunately worse in winter than in 

 summer ; but, nevertheless, the force exerted even by a 

 summer gale of wind on a tree in full foliage is enormous. 

 It is probable as Lord Avebury (Sir John Lubbock) has 

 suggested, that many cases of divided leaves are 

 to be explained by the necessity of offering only a 

 slight resistance to the wind. The Rowan {Pyrus 

 Aucuparid) has a flexible midrib and each leaflet can 

 bend independently on its own little stalk. The Ash 

 is particularly interesting to watch on a windy day. 

 The branch bends over till it is as nearly as possible in 

 a line with the direction of the storm. The wind then 



(B7) K 



