CLIMBING PLANTS 
173 
(p. 1 14) ; in the tropics many hook-climbers grow to a great 
size and have stem- or leaf-structures modified into hooks, 
e.g. Calamus, Desmoncus, Caesalpinia. Cf. also Rosa, 
Pereskia, Capparis, Lycium, &c. These hooks are not 
sensitive to contact like those described in the preceding 
section. 
IV. Root-climbers climb by aid of special adventitious 
roots upon the stems. These are not usually sensitive to 
gravity but show a marked negative heliotropism, which 
causes them to follow out all the crannies and irregularities 
of the surface upon which they creep, and thus to firmly 
attach themselves to it. Instances are ivy (Hedera), many 
Araceae, Hoya, Tecoma, Norantea, Ficus sp., Piper sp., 
and many ferns. The aerial roots of Philodendron sp. 
twine as they descend. Ivy and others have dimorphic 
shoots [cf. Salacia, &c.). 
Anatomically, climbing plants present many features of 
interest. The stem is very thin compared to its length, 
but grows slowly in thickness to supply the new leaves with 
water. The growth is commonly 4 abnormal J and results in 
many cases of tropical climbers (lianes) in stems of the most 
remarkable shapes — flat, twisted, corrugated, &c. — which 
may be seen in most museums. 
Creeping plants, in which may be included those with 
horizontal rhizomes (p. 153), are like climbers in throwing 
the weight upon outside supports, and grow but little in 
thickness. They are common in meadows, and in the 
undergrowth of woods. 
Epiphytes 1 cling to other plants for support, but are 
not parasitic upon them, and are not usually attached to 
the soil. In the temperate zones they are rare — except 
among Algae, Mosses and Liverworts — but in the wetter 
forest regions of the tropics they abound, perched upon the 
branches and even leaves of other trees and plants, forming 
a marked feature in the vegetation. Being usually small 
herbs they thus obtain favourable situations without the 
expenditure on stems needed by erect plants and even by 
climbers, but on the other hand the obtaining of food 
1 Schimper, Die Epiphytische Vegetation Amerikas, Jena, 1888; 
Goebel, PJianzenbiologische Schilderungen ; Willis and Burkill, Flora 
of Pollard Willo 7 vs, Proc. Camb. Phil. Soc. 1893. 
