282 ABSORPTION-CELLS ON LEAVES. 
similar contrivance is also exhibited by the leaves of alpine roses and those of the 
American Bacharis. For instance, on the under surface of the leaves of the Alpine 
Rose (Rhododendron hirsutwm) there is a large number of discoid glands (fig. 54°), 
each of which is supported on a short stalk and sunk in a little hollow (fig. 54) 
The cells composing the gland are arranged radially, and contain slimy, resinous 
matters capable of swelling up. These contents are also excreted, and then cover 
the entire glandular dise, and often even the whole surface of the leaf in the form 
Fig. 54.—Absorption of Water by Foliage-leaves. 
1Grooved rachis of the ash-leaf. Section through the same; x30. 3 Peltate group of cells from the groove. 4 Section 
through the base of a leaf of the Dwarf Gentian; x20. 5Under side of a leaf of Rhododendron hirsutum; x30. ®Section 
through a leaf of Rhododendron hirsutum. 
of a light-brown crumbly crust. When drops of rain fall upon Alpine Rose leaves, 
the whole of the upper surfaces, in each case, is in the first place moistened; but 
without delay, and partly through the action of the hairs fringing the margin, the 
water soaks on to the under side of the leaf. As soon as it reaches the glands it is 
taken up by the crumbly incrustation mentioned above, which swells up in con- 
sequence. The little cavities in which the glands are situated also fill with water, 
and each gland is then immersed, as it were, in a bath, and able to absorb as much 
moisture as is required. Owing to the glands being invariably developed above 
the vascular bundles of the leaf (see fig. 54°), the water that is absorbed can be 
conducted without delay by them to the places where it is required. As soon as 
the leaves of alpine roses become dry again, the mass of resinous mucilage again 
