i66 LIFE : OUTLINES OF GENERAL BIOLOGY 



the epiphytes have often water-reservoirs which enable them to 

 survive the dry season; the terrestrial species, though rootless like 

 all the others, have little processes or rhizoids which descend into 

 the ground, esjxcially at the base of the flower-stalk, and serve to 

 steady the latter as well as to absorb water. 



Allied to Utricular ia is the rarer Genlisea, found in marshy places 

 in Brazil, Cuba, and Angola. It is rootless except in the seedling, 

 and the upright stem is beset with two kinds of leaves. The ordinary 

 foliage-leaves are spatulate, and the others, far fewer, are strange 

 traps. Each is ti|)ix:d with two spirally twisted glandular arms, 

 which secrete nuicus, and are intricately equipped with hairs and 

 processes which allow of the entrance of very small animals and 

 make exit next to imix)ssible. Then follows a long neck, also lined 

 internally with downward directed hairs, and near the base there is 

 a little bladder-like expansion. These strangely transformed leaves 

 grow into the swampy ground, and serve to anchor the rootless 

 plant, and also to entrap minute animals. Goebel points out 

 that the Butterwort is near the starting-point of a series, with 

 Genlisea diverging in one direction and the various Utricularias 

 in another. 



PERCHED PLANTS OR EPIPHYTES.-In North Temperate 

 countries the most familiar epiphytes are certain lichens, which often 

 spread profusely on the branches of trees. But there are also a few 

 unicellular Alga*, of the Pleurococcus tyjx", which make the stems 

 green, especially in damp weather. Higher on the scale are the 

 tree-mosses, and here and there one sees a pol}TX)dy fern perched 

 far above one's head. In the cleft of a tree, where there has been 

 an accumulation of dust and humus, and occasionally a dead bird 

 or the like, there is the beginning of soil, and such plants as Herb 

 Robert [Geranium robertianum) and s}x>cies of Willow-herb (Epilo- 

 bium) may be seen in flower. But these flowering plants are only 

 casual epiphytes. 



Constant epiphytes are characteristic of humid tropical forests, 

 and many of them belong to the Orchids, Aroids, and Bromehas. 

 They obtain their necessary water from rain trickling down the 

 branches, or directly from the water va]X)ur of the air; and the 

 mineral salts are obtained from dust particles and sometimes from 

 a slight accumulation of organic debris. Very characteristic is th<- 

 widely distributed "X'egetable Honsehair" or "Spaniards' Beard" 

 [Tillandsia usneoiJcs), which hangs down in long silvery-grey 

 streamers from the high branches. In this sjx^cies there arc neither 

 leaves nor roots, the whole ])lant being reduced to the numerous 

 long thread-like stems. While many epiphytes, like the one just 

 mentioned, are jx-rrhed on tree- tops, they occur at all levels to a few 

 feet above the grcnmd This of itself is enough to suggest that the 



