326 ZONES AND REGIONS [Pt. Ill, Sect. I 



widened out below like spoons, and fit so closely together that, like water- 

 tight tanks, they collect rain-water, of which a full liter may descend from 

 one of the larger forms on to a careless collector : besides this, like the less 

 tight leaf-funnels of the nest-epiphytes, they contain all kinds of detritus 

 of mineral, vegetable, and animal origin, and this, as the vigorous growth 

 of the plant shows, affords a fertile nutritive substratum. The rosettes of 

 leaves spring from a short, gnarled system of axes fixed to the substratum 

 by short thin roots, which are, however, as strong as wire (Fig. 165). 



The roots consist almost exclusively of thick-walled fibres and take no 

 part in the nutrition, as has been proved experimentally. The absorption 

 of nutriment takes place entirely through the leaves, by means of peltate 



Fig. 166. Vriesea. Scale-hair. Fig. 167. Tillandsia usneoides. Scale-hair. 



Magnified 340. Magnified 375. 



scale-hairs (Fig. 166), which are situated in particular on the dilated base 

 of the leaf that is usually under water. If there should be no water on 

 the surface of the leaf, these hairs contain air alone ; every drop of water, 

 however, is at once absorbed by them, just as by the velamen of orchids, 

 and it reaches the interior of the leaf owing to the activity of passage-cells 

 that are rich in protoplasm (Fig. 167). 



From this type, which is exhibited in a pure form in particular by 

 species of Vriesea, Aechmea, and Nidularium, not inconsiderable deviations 

 occur in many species of Tillandsia, especially Tillandsia usneoides (Figs. 

 168, 169). This most remarkable of all epiphytes, often completely 

 covering the trees in tropical and subtropical America, consists of shoots 

 often far more than a meter in length, thin as thread and with narrow grass- 

 like leaves, and only in early youth fixed to the surface of the supporting 

 plant by weak roots that soon dry up. The plants of Tillandsia owe 

 their attachment to the fact that the basal parts of their axes twine round 

 the twigs of the host. The shoots are covered all over with scale-hairs, 

 which in structure and behaviour resemble those of other Bromeliaceae. 

 The dispersal of the plant takes place less by seed than by vegetative 

 means, through the transport of severed shoots by the agency of the 

 wind or of birds, which readily utilize the fragments in the construction 

 of nests. 



