ABSORPTION OF RAIN AND DEW BY THE FOLIAGE-LEAVES. 229 
tion of water is not very considerable. But it often happens that the uppermost 
cells of a septate hair are developed into absorption-cells. The terminal cell is then 
usually spherical or ellipsoidal and larger than the rest, or else this cell is divided 
into two, four, or a greater number of cells, which together form a little head, whilst 
the lower cells constitute a stalk supporting it (see fig. 53° and 534). In botanical 
terminology structures of this kind are named capitate or glandular hairs. The 
protoplasm in the cells of the head is, for the most part, of a dark colour, and the 
GDgE RES 
Fig. 53.—1 Hairs from stem of Stellaria media; x110. 2 Lowest cells of the same hairs; x200. 3Capitate hairs of 
Centaurea Balsamita; x150. 4Capitate hairs of Pelargonium lividum; x 150. 
cell-membranes are readily permeable by water, which is attracted with great 
energy by the cell-contents. The cell-membrane is often very thick, it is true, but 
as soon as water comes into contact with it the outer layer is discarded, the inner 
layers swell up and the water passes through these swollen layers into the interior 
of the cell. This happens, for instance, in many pelargoniums and geraniums, 
wherein the capitate cells go through a process of excoriation on every occasion of 
the imbibition of water (see fig. 534). In other plants the walls of the capitate 
cells are everywhere thin, and not only do the cell-contents consist of a viscid gum- 
like mass, but the external surface of the wall is also covered by a layer of viscid 
excretion. In many cases the viscid matter excreted by the glands spreads over the 
entire surface of the leaf, so that the latter feels sticky and looks as if it were 
