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 



Li 



Fig. 166. Vriesea. Scale-hair. 

 Magnified 340. 



Fig. 167. Tillandsia usneoides. Scale-hair. 

 Magnified 375. 



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

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

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

 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-cell 

 that are rich in protoplasm (F"ig. 167). 



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

 species of Vriesea, Aechmea, and Nidularium, not inconsiderable deviation! 

 occur in many species of Tillandsia, especially Tillandsia usneoides (Fig;; 

 168, 169). This most remarkable of all epiph}-tes, often completelj 

 covering the trees in tropical and subtropical America, consists of shoo* 

 often far more than a meter in length, thin as thread and with narrow gras: 

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

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

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

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

 which in structure and behaviour resemble those of other Bromeliacea 

 The dispersal of the plant takes place less by seed than by vegetati^ 

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

 \\ind or of birds, which readily utilize the fragments in the constructic 

 of nests. 



