348 WINDOW GARDENING, AND [chap. xi. 
arises principally from the habit that most 
poor people have, of setting their plants out 
in the rain whenever there is a shower. 
This not only clears the leaves of dust, and 
opens the stomata or breathing pores, but 
gives the plant abundance of fresh air. 
Without a sufficiency of air and light, plants 
will soon become weak and sickly, and their 
leaves will turn yellow; but if a little fresh 
air be given to them every day when the 
temperature is not too cold, they will grow 
quite as well in a room as in a green-house. 
Another reason why plants kept in rooms 
are generally unhealthy, is, that they are 
watered in a very irregular manner. Some¬ 
times they are suffered to become so dry that 
the mould in which they grow will crumble 
under the pressure of the finger, and the 
spongioles of the roots are quite withered; - 
and then a profusion of water is given to 
them, quite cold from the pump, though 
they have probably been standing in a tem¬ 
perature of from 60° to 70°. As a climax, 
part of this water is suffered to remain in 
the saucer for a day or two, till even the 
healthy part of the roots is thoroughly 
