158 PLANT LIFE 



Many of the other members of the natural 

 order (Bromeliacese) to which the pine-apple 

 and the tillandsias belong, are variously 

 specialised with respect to water supplies. 

 The large bromeliad of tropical America 

 possess clasping roots which fasten the short 

 stem with its, relatively speaking, immense 

 crown of foliage, on the branch of the tree 

 which serves as its perch. The roots have little 

 if anything to do with absorption, a function 

 which has been almost entirely taken over 

 by the tillandsia-like hairs which are found 

 on the upper surfaces of the leaves. The 

 latter form remarkable cisterns in which 

 water is collected and stored, and from which 

 it is absorbed by the hairs that are especially 

 numerous where the water is stored. Each 

 leaf is a long, more or less strap-shaped body, 

 with the edges curving towards each other in 

 the middle portion, thus forming a sort of 

 gutter. Nearer the base, the leaves press 

 tightly on each other and thus constitute 

 the cisterns. Water falling on the upper 

 surface of the leaf is directed into them by 

 means of the gutter-like curvature just 

 described, which causes the rain to run down 

 to the centre of the crown, instead of dripping 

 off as it does from most leaves. The efficient 

 manner in which the foliage is arranged to 

 form cisterns may be gauged by the fact that 

 water plants are fairly often found growing 

 and flourishing in the water thus collected 

 and retained. 



