GEOGRAPHICAL DISTRIBUTION OF PLANTS. 
31 
and by the leaves assuming a pale and sickly appearance ; and if 
it is withheld for any great length of time, will certainly perish. 
As a general criterion to judge of the nature of such plants 
that require the full power of the sun’s rays, we find that those 
of a juicy or succulent substance, which produce a great quantity 
of leaves, and expose a large surface to the atmosphere, require a 
great intensity of light, and are always found in those situations 
where a great supply is given to them. Those plants which are 
very porous, and are abundantly furnished with organs of evapora¬ 
tion, and those which are nearly destitute of foliage, are generally 
found in shady places, and abound most in the recesses of tropical 
forests, where the direct rays of the sun never penetrate. For 
the elucidation of the above remarks, I think it necessary to allude 
to the plants which were found at Chatsworth, to bear out the 
subject. The Cacti, Opuntia, Mysembrianthemum, and all plants 
of that succulent nature, require a great intensity of light; 
Orange Trees, instead of being kept in dark houses, and exposed, 
as they generally are in autumn, to the direct rays of the sun, 
which must be Injurious to them, by such sudden transitions 
of light, on the general principles recommended, ought to be 
more exposed to the rays of solar heat. Geraniums may be 
classed with the other plants which receive great benefit from a 
full exposure to the influence of light; while Camellias would be 
found to succeed best in a comparatively shady situation, where 
they flower well, and attain that luxuriance of foliage which is 
one of their chief ornaments. Hothouse Climbers are found in 
their native countries climbing on the branches of trees in large 
jungles where the rays of the sun never penetrate ; and instead 
of being exposed as they generally are in our stoves, they would 
be found to succeed better in more shaded situations. 
In the successful cultivation of plants or fruits, it is necessary 
to erect a house for them which w r ould be properly adapted to the 
habits of the plants or fruits; and that they should receive the 
rays of light vertically, and not obliquely ; and to form such a 
slope of roof as shall be at right angles to the sun’s rays, at what¬ 
ever season it is intended to ripen the fruit. The angle of 45° 
is generally used by gardeners ; and in the latitude of London 
the rays would be perpendicular in the early part of April and in 
September. To have the greatest benefit of the sun’s rays in 
ripening fruits in July, an angle of 34° is best for the purpose. 
