1884.1 
535 
On Tropical Epiphytes* 
but few vessels. . The green of the surface is interrupted by 
white stripes which mark out parts of small permeability for 
water, but great permeability for gases, and seem to replace 
tne apertures of ordinary assimilating organs. 
In the second group, where the roots subsequently always 
reach the ground, the great expenditure of material does not 
correspond to the objedt gained, as the connection of such 
Epiphytes with the soil is but imperfeCt. In some cases, 
however, a step is taken to perfect development; the two 
1 unctions of nutrition and fixation are allotted to different 
loots. I he clinging roots, destined to secure the plant in its 
J r , e stron ? I y negatively heliotropic, but are not notably 
aneCted by gravitation. They grow slowly, seldom reaching 
the length of two feet, and die off like tendrils if they do not 
soon meet with a. support. As soon as such a one is found 
they creep along it or twine around it. The vascular bundle 
consists of lignified thick-sided fibres. The nutritive roots 
are often negatively heliotropic, and are always under the 
influence of gravitation, being strongly attracted to the earth. 
They glow lapidly to an unlimited length. In a short time 
they can reach the soil from a height of 100 feet, and there 
they ramify abundantly. The vascular bundle consists of 
tracheae with a wide opening and of sieve-tubes, whilst the 
mechanical elements are less important. 
The same two classes of roots may likewise be distinguished 
m the Epiphytes of the third group, though the differentia- 
tion of the two classes is here less decided. The clinging 
roots are negatively heliotropic, and possess a great tensile 
power. The nutrient roots are chiefly concerned with the 
utilisation of nutriment situateakws the isodiametric system 
of roots. They are therefore positively heliotropic, and are 
directed upwards. But contact occasions many changes in 
the direction of their growth, as well as anastomoses, forming 
an inextricable network. Anatomically speaking, the two 
masses cf roots differ little. The nutritive roots absorb 
nourishment, and the cling-roots transmit it to the shoots. 
In Anthurium Hugelii the root system, more than a cubic 
foot in bulk, surrounds and overtops the short stem, and 
sends, numerous ramifications into the humous mass of 
decaying vegetable matter which accumulates among the 
crown of leaves. 
In the fourth group the roots disappear altogether, or are 
reduced to mere organs of adhesion. Here we find only the 
Bromeliacese. The simplest arrangement occurs in Tillandsia 
usneoides. This plant, entirely rootless, hangs down from 
the branches of trees in bundles resembling the tails of 
