HOUSE PLANTS. 
89 
appearance shows that the plant has been in impure air or other¬ 
wise improperly treated. Sulphur or camphor will effectually 
remove this mildew ; and a scaly insect of .the coccus tribe, which 
appears occasionally on oranges, camellias, and similai plants, 
may be removed by a sponge and water. 
Many persons have a dislike to plants in houses as being un¬ 
healthy ; and as this dislike is in a great measure groundless, we 
may notice it. Dr. Priestley was the first to show that the leaves 
of plants absorb carbonic acid gas by their upper surfaces, and 
give out oxygen by their under ones, thereby tending to purify 
the air in as far as animal life is concerned ; because carbonic acid 
gas is pernicious to animals, and oxygen is what that life acquires. 
It is in the light, however, that these operations are carried on ; 
for in the dark, plants give out carbon ; and this may be one 
reason why plants grown in the dark have little or no charcoal in 
their substance. It does not appear, however, that any of the 
scentless products given out by plants are injurious to human 
beings ; because those who live among accumulated plants are 
not less healthy than others ; though many persons feel dislike 
and even pain from the odors of particular plants, in a way not 
very easily accounted for. 
On the Continent in general, and in France and Germany in 
particular, flowers of all sorts, but particularly the most fragrant, 
are admitted into the saloons, chambers, and even bed rooms of 
people of all classes ; and they, rather than complain of any ill 
3flects arising from their presence, complain more of the difficulty 
of procuring them in sufficient abundance. The flowers most in 
demand for the chambers of the French and Germans are, oranges, 
jasmine, carnations, honey-suckle, mignonette, olive, rocket, rose, 
violet, wall-flower, rosemary, stock, lavender, savory, oleander, 
hyacinth, lilac, syringa, heliotrope, narcissus, &c., all sweet-smell 
