TRE ALOE 
205 
have long intermissions, are admirably provided by their 
succulent leaves and stems for the conditions under which 
they exist. The cuticle, or thin skin, which covers every 
part of a plant, is, in those which contain a great quantity 
of pulpy material, formed so as to imbibe moisture with 
peculiar facility, and to evaporate it very slowly. If a 
leaf of an aloe be separated from the parent plant, it may 
be laid in the sun for several weeks without becoming 
entirely shrivelled ; and even when considerably dried, by 
long exposure to heat, it will, if plunged into water, be- 
come in a few hours plump and fresh. 
Plants thus formed and situated derive very little sus- 
tenance from the soil on which they grow ; depending 
chiefly upon the atmosphere, which they imbibe through 
their leaves. This may be seen in the yellow stone-crop 
of the old wall, and the house-leek, which our forefathers 
carefully planted among the tiles on the roofs of houses, 
under the idea that it preserved them from thunder and 
lightning. Either of these plants will grow on the small 
quantity of soil which fills up the crevices of a brick wall, 
or upon a stone grotto, and flourish there as well as in the 
mould of a garden. 
The different species of cactus, also, which produce 
their handsome scarlet or pink rose-shaped flowers in the 
conservatories of this country, are never found wild but 
in a warm and very dry situation, where little food can be 
extracted from the earth. Of the same nature are those 
singular productions of the African desert, the carrion- 
flowers — Stapelia. These plants scent the air to a great 
distance with their disgusting odours of carrion, and at- 
tract the flesh-fly to the conservatory in England in which 
they are found. 
The species termed the warty carrion-flower (Stapelia 
verrucosus) is sometimes seen in the hothouses of this 
country. 
The cactus, in its native climate, affords instances of 
immense vegetable growth, and is even planted in the 
neighbourhood of forts, as affording by its spiny leaves a 
better protection than a guard of human sentinels. 
The nourishment of plants in general is effected by 
means of their roots and leaves. The small fibres of the 
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