228 



ABSORPTION OF RAIN AND DEW BY THE FOLIAGE-LEAVES. 



by rain and retain a considerable quantity of water. The water that they cannot 

 hold they conduct downwards to the ciliate axils of the next lower pair of leaves, 

 where it is drawn through the lash-like hairs in due course and collected into a 

 ring of water surrounding the node (see fig. 52^). If this accumulation of water 

 becomes so voluminous and heavy that it cannot any longer be retained by the 

 fringe of lashes, the surplus glides on to the unilateral ridge of hairs on the adjacent 

 internode down to the pair of leaves below. Accordingly, after a shower every 

 node from which leaves arise is seen to be inclosed in a water-bath, and the hairy 



Fig. 52. — Hairs and Leaves which retaiu Dew and Rain. 

 Dwarf Gentian {Gentiana acaulis). * Lady's Mantle {Alchemilla vulgaris). 3 Chickweed (Stellaria media). 



ridges also are so soaked with water that they look like edgings of glass. All the 

 individual cells in each of the hairs are full of protoplasm and cell-sap, but only the 

 lowest, which are very short, really act as absorption -cells. When these cells 

 become at all relaxed in dry air, the fact is indicated by the appearance on the 

 external cell- wall of fine striae (see fig. 53 ^ and 53 2). The protoplasts inhabiting them 

 attract water, and after being relaxed in the manner referred to the cells regain 

 their turgidity on being wetted, whilst the fine wrinkles on the outer membrane are 

 in consequence immediately smoothed out. Although the upper cells of the hair 

 possess a less thick cuticle, they, on the other hand, seem not to absorb any water, 

 but to serve rather to conduct it by their surfaces. 



This case is, as we have said, comparatively rare, and the corresponding absorp- 



