ABSORPTION OF RAIN AND DEW BY THE FOLIAGE-LEAVES. 225 
into a mouldering mass. But as soon as they perish other new air-roots, covered 
with golden-brown velvet, make their appearance and take their place. These aérial 
roots never reach the ground or adhere to any substratum, so that their hairs 
cannot contract an organic connection with a solid body. It is consequently also 
impossible in this case for the root-hairs to draw moisture from the soil in the 
capacity of absorption-cells. 
These root-hairs, however, are scarcely ever in a position to take up even the 
atmospheric deposits. The various species of Philodendron and the other epiphytes 
referred to, have large leaves which cover the air-roots hanging from the stem like 
umbrellas, and every tree-fern also bears at the top of its stem a tuft of great 
fronds, which prevents falling rain from wetting the aérial roots. Moreover, the 
very plants whose air-roots exhibit a velvety coating occur in woods where the 
tops of the trees arch over the ground in lofty domes, and form a sheltering roof 
against deposits from the atmosphere. On the other hand, the air within these 
forests is saturated with aqueous vapour, and it is certain that the velvety roots 
have the power of condensing vapour, and that the root-hairs instantly suck up the 
condensed water and convey it to the deeper-lying layers of cells. The truth of 
this has been established by the results of repeated experiments. Thus, air-roots of 
the tree-fern Todea barbata, after being transferred from moderately damp air 
into a chamber full of vapour, condensed and absorbed in the space of twenty-four 
hours water amounting to 64 per cent of their weight. There is, therefore, no doubt 
that water may be acquired in this way also by plants, even though the instances 
may not be very numerous. All plants in which this kind of water-absorption has 
been hitherto observed grow in places where the air is very moist the whole year 
round, and where there is also no risk of the temperature falling below freezing- 
point. Under other conditions, especially in places where the air is periodically 
very dry, these plants would not be able to survive; for, although they possess 
organs for the condensation and absorption of water, they have no means of protec- 
tion against the desiccation of these organs. 
ABSORPTION OF RAIN AND DEW BY THE FOLIAGE-LEAVES. 
The idea that plants absorb with their roots such water as they require is so 
intimately associated with our whole conception of plant-life, that this process is 
commonly adduced for the purpose of analogies of the most various kinds, and one 
looks upon the water-absorption effected by aérial roots in the manner just described 
really as a thing to be expected, notwithstanding the fact that in this case, as the 
above account shows, the phenomenon is not so simple as is usually supposed. We 
now turn to the consideration of land-plants. If the leaves of plants cultivated in 
pots become flaccid, water is poured as quickly as possible upon the dry soil with a 
view of supplying the roots which ramify in it with moisture. Nor does the result 
fail to be produced. Ina short time the foliage becomes fresh and elastic again, 
the zu ee discharged their function. Even in the open air, it is mean 
