THE WINDOW GARDEN 3 
If plants are to develop symmetrically, they must 
be turned frequently, but it is usually best to let the 
leaves occupy the same position with reference to the 
light from day to day. Plants will not thrive if they 
are changed so that strong sunlight falls on the under- 
side of the leaves. 
Fresh air containing the required amount of moisture 
is as important for plants as for children; neither can be 
kept in health without it. But drafts must be avoided ; 
no cultivated plant can be submitted to a draft for any 
length of time without injury to its foliage or blooms. 
Special care must be taken in the spring, when the 
weather may change completely in the space of an hour. 
In most schoolrooms the dryness of the air, caused by 
artificial heat, must be counteracted by keeping the 
water pan in the furnace air chamber well filled. In 
the case of steam-heated rooms the normal amount oi 
moisture may be obtained by allowing steam from the 
radiator valves to escape at intervals. 
Dry heat absorbs the moisture from the foliage, and 
the fine dust that is always afloat in the excessively dry 
schoolroom atmosphere fills the stomata (the openings on 
the underside of the leaves, through which they obtain 
air) and causes the plants to become sickly and subject 
to the attack of insects. 
The ordinary temperature of from sixty-eight to 
seventy degrees, which may go as low as fifty overnight, 
is suitable for nearly all house plants. Large school 
buildings should never be permitted to have a lower 
