EPIPHYTES 121 
that the main leaf-axis and its branches may all alike 
take part in attaching the plant to a support. There is 
no doubt that a similar general sensitiveness preceded, 
in evolution, that localized and specialized sensitiveness 
which, in other climbers, is confined to the tendrils. 
This sensitiveness, which accompanies partial etiolation in 
weak light, and which makes the evolution of the tendril 
possible, is probably due to the fact that etiolated stems 
and shoots, through their rapid growth, have soft tissues 
with no strong woody elements during their sensitive 
period. Sensitive movements can only be associated with 
organs whose tissues consist of thin-walled cells, turgid 
with water. 
There are not many native climbers in temperate 
climates. In tropical rain-forests, tree-growth is so 
luxuriant that the forest-floor is always plunged in partial 
gloom. Climbers with great twisted woody stems sprawl 
over the undergrowth, and loop themselves from tree to 
tree, climbing towards the light they need so much. The 
only woody climbers (lianes) we possess are the clematis, 
honeysuckle, and ivy. 
Epiphytes.—These are plants which pass their lives 
perched upon the elevated parts of other plants, chiefly 
the branches of trees. They are anchored to their sup- 
ports in various ways, usually by clasping roots. As a 
result of their position, they have a precarious water- 
supply, and invariably show xerophytic characters. The 
most common epiphytes are found among the lower plants, 
—lichens, liverworts, mosses, and ferns. The most abun- 
dant epiphyte everywhere is the lichen, which shows 
wonderful adaptations to extreme conditions. Generally, 
however, epiphytes are only found in moist shady places, 
and this is especially true of the flowering epiphyte, 
which is rare in the temperate regions of the world. In 
the Tropics, on the other hand, they form a feature of the 
vegetation of the dripping forests, the home of the 
epiphytic orchids and bromeliads. In this country we 
have no true flowering epiphyte. Accidentally, however, 
many plants are epiphytic. In humid mountain glens 
we may often see plants growing on other plants—ashes 
on oaks, stonecrop on the aged branches of trees, and 
various ferns, especially the polypody. The true epi- 
phyte, however, is a xerophyte amid vegetation markedly 
