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J. C. Th. Uphof. 
colloidal layer, which contributes very much towards its protection 
from extreme transpiration ; plants from more favourable situations 
do not possess such a layer. This can easily be detected with low 
powers of the microscope, and readily removed from the underside 
of the ventral leaves, clearly showing the imprints of the 
elongated cells of the epidermis. In contact with water the 
colloidal layer very quickly absorbs the liquid, losing the cell 
imprints, increasing five to six times in size, and slowly forms a 
structureless gelatinous substance. The colloid absorbs a weak 
solution of eosin, staining red in a short time, while the surrounding 
water remains pink. Water evaporates more slow from this 
gelatinous matter than pure water would do. This fact can be 
readily observed on the plant. There is no doubt that the colloidal 
layer has two functions to perform; in the first place it protects 
the plant against extreme heat, through minimizing transpiration 
by covering such parts of the plants by a hard substance; in the 
second place it absorbs the water after a shower or heavy dew and 
retains it longer than if the plant were without the gelatinous 
cover. The thickness of this colloidal layer, when dry, is 
sometimes thrice that of the leaf which it covers. 
In S. lepidophylla, the chlorophyll-free margins of the dorsal 
leaves toward the apex are broad (Fig. X. 3) and reflect the light; 
the author observed that this is of much importance during the 
early development of the young dorsal leaves toward the growing 
point of the stem, since each half developed leaf is protected 
against the light by the broad margin of its neighbouring leaf. 
This feature is only of use when the branches are spreading in 
a horizontal direction, as they do when moistened. 
The leaves of S. Pringlet have instead of a broad chlorophyll-free 
margin, a long awn at the apex (Fig. X, 1, 2); when the leaves are 
young, the awns of several leaves are situated close to each other 
toward the top of the shoot (Fig. I, 4), thus protecting the very 
young leaves. Also the growing point of the main stem, in the 
centre of the plant, is thus thoroughly protected by the awns. At 
a later stage the awns become valueless. 
When it rains the cluster-balls soon unfold. This movement 
manifests itself in 1 to 2 hours, the whole plant becoming a flat 
rosette in 10 to 12 hours. The absorption of water by the tissues 
increases the weight of the plant by approximately 50 per cent, as 
is shown from the following table. 
