23 
of some plants, have .the power of absorbing water. It 
1s not an uncommon practice to spray the leaves of plants 
in the greenhouse when they are shaded, and also in the 
open when the sun is no longer upon them and their sub- 
sequent recovery, if they were drooping before, is attri- 
buted to their having absorbed water. This is however 
not the case. The spraying of the leaves, besides cooling 
the foliage, which is often considerably heated by the sun, 
has the effect by the evaporation of the water to render 
the atmosphere around the plant moisture-laden, where- 
fore the transpiration of the leaves is at once decreased. 
It is this decrease of transpiration and not absorption by 
the leaves which causes the revival of the plants. No 
leaves with an impervious covering can take in water and 
there are very few leaves which are not so protected. 
Mosses and Filmy Ferns alone among leafy plants can 
take in water through their leaves, which are adapted to 
growth in moist if not dripping conditions. 
It is interesting to note that when the stomata are 
closed and transpiration is impossible, some plants are still 
able to get rid of their superfluous water. At night the 
leaves of the Nasturtium and the Fuchsia for instance are 
able to force out little drops of water through water-pores, 
which are found at the termination of their veins. Many 
grasses, too, have water-pores at the tips of their leaves, 
and the drops of water exuded by them often look like the 
formation of dew. 
When growing in very dry soil or in hot arid climes, 
plants may experience a great difficulty in supplying their 
leaves with water, often during a very prolonged period. 
In such cases many remarkable deviations from the normal 
struciure are produced, with the object of protecting the 
leaves against drought. In most cases the leaves are small, 
often reduced to mere scales or needle-shaped structures. 
Such are the leaves of many of our moorland plants grow- 
ing in sandy, well-drained soil and exposed to strong and 
drying winds. In still more arid regions the leaves may 
disappear altogether, and we get such curious plants pro- 
duced as the fleshy Cacti of the New World and the 
succulent Euphorbias (Spurges) of the Old World. In 
both of these groups of plants the green stems undertake 
the process of assimilation, and they also store up sufficient 
water during the wet season to enable the plant to last 
out during a prolonged drought: 
