152 PLANT LIFE 
to bring out the more salient features of this 
remarkable structure, which is generally known 
as the velamen of the orchid root (Fig. 19). 
The cell walls of the velamen are strength- 
ened by bars of thickening, which gives them 
a spiral or netted appearance under the 
microscope. The function of the velamen 
as a whole is to act as a sort of sponge which 
soaks up liquid falling on it with extreme 
rapidity. Thus the plant is able quickly to 
replenish its supplies of water during a shower. 
In many orchids the bases of the stems and 
sometimes the leafy joints are swollen with 
the so-called ‘“ pseudobulbs,” which form 
additional storehouses for the water thus 
obtained. During the periods which inter- 
vene between the rains, the plant often 
throws off its leaves, its flowers drawing on 
the water supplies stored in the pseudobulb. 
The surface of the latter becomes more and 
more wrinkled as its storage cells become 
depleted of their water contents. 
The roots, although specialised in the way 
described above, have retained, in many in- 
stances at any rate, the power of growing like 
ordinary ones if they should happen to pene- 
trate the substratum. This sometimes occurs 
when there is sufficient vegetable detritus 
caught in the orchid clump, or when the root 
penetrates a piece of damp rotten wood. 
Root-hairs are then produced, and the velamen 
may be scarcely produced at all. 
It is a remarkable fact that some of the 
