ABSORPTION-CELLS ON LEAVES. 233 
forms a dry erust over the glands and proteets their tender-walled cells from too 
great evaporation. 
Very remarkable also are the structures adapted to absorption on the leaves of 
saxifrages belonging to the group Aizoon, and on those of a large proportion of the 
Plumbaginee. The saxifrages in question have little depressions visible to the 
naked eye upon the upper surface of the leaves behind the apex, and along the 
margins. When the margin is dentate or crenate, as, for instance, in Saxifraga 
Fig. 55.—Absorptive Cavities and Cups on Foliage-leaves. 
1 Leaf from a shoot of the Aspen. 2The base of this leaf; x3. %Section through an absorption-cup; x25. 4 Leaf of 
Acantholimon Senganense. Section through part of this leaf; x110. © Leaf of the Evergreen Saxifrage (Saxifraga 
Aizoon). 7Two teeth from the margin of this leaf. The absorptive cavity in the upper tooth incrusted with lime; the 
lower one with the incrustation removed. %Section through a tooth from the leaf and its absorptive cavity; x110. 
Aizoon (see fig. 55°), one of these cavities occurs in the middle of each tooth. 
The cells forming the outer edge of the tooth or scallop are always much 
thickened, firm, and rigid; but the median portion of the leaf as a whole is fleshy, 
and composed of a bulky large-celled parenchyma. The vascular bundle, after 
entering the leaf at its base, divides into a number of lateral bundles which either 
run towards the margin without further ramification (as in Saxicesia), or else 
form a net-work by uniting one with another in their course (as in Sawifraga 
Aizoon). These lateral bundles terminate in the marginal teeth of the leaf and 
immediately beneath the little cavities which occur there, whilst the extremity of 
each bundle swells into a knob or pear-shaped enlargement strongly resembling 
the roundish groups of spirally-thickened cells in the tentacles of the Sun-dew 
