HOUSE PLANTS. 
79 
air than plants which have the leaves small or of delicate texture. 
Some tribes, as the heaths, the JEpacridece , and the whole race of 
pinnate-leaved and papilionaceous flowered plants, are wholly 
unfit for house culture. 
TREATMENT OF HOUSE PLANTS. 
Water, heat, air, and light, are the four essential stimulants to 
plants; water, heat, and air, to promote growth ; and light to 
render that growth perfect. 
Water, heat, and air, man can command at his pleasure by 
artificial means ; but over light, as an element of the perfect 
growth of plants, we have less control. To be beneficial to plants, 
light must come directly from the sun; and therefore the plants 
should be so placed, as that it may act upon them with as little 
as possible of that refraction and decomposition which it suffers 
when it passes obliquely through glass, or any other medium 
except the air. Plants grown in the open air, and with such free 
exposure to the light as their habits require, not only develop all 
their parts in their proper form, but their leaves, flowers, and 
fruits, have their natural colors, odors, and flavors. Plants ex¬ 
cluded from light have not their natural color, odor, nor flavor, 
they make little or no charcoal in the woody part, the leaves are 
not green, and if they do flower and fruit, which is rarely the 
case, the flowers are pale and scentless, and the fruit is insipid. 
This has been proved by many experiments, of which the blanch¬ 
ing of celery and endive by earthing up, and that of a cabbage 
by the natural process of hearting, are familiar instances. A 
geranium placed in a dark room becomes first pale, then spotted, 
and ultimately white; and if brought to the light it again ac¬ 
quires its color. 
Tf plants kept in the dark are exposed to the action of hydrogen 
gas, they retain their green color, though how this gas acts has 
