52 WINDOW GARDENING. 



VENTILATION. 



This must not be neglected; it is as essential to the 

 health of the plant as to the human organization. The best 

 method of providing it is to open the top of the window when 

 the sun's rays are hottest on the plants. The quantity of 

 air to be given must be proportioned to the outside tem- 

 perature. In cold, cloudy days, but little, and often none, 

 should be given. Care must be taken never to allow a 

 direct stream of cold air to blow upon any plant. 



WASHING. 



This must be done frequently. A plant breathes like an 

 animal, and not through one mouth, but thousands. As is 

 well known, the plant draws up its food from the soil 

 through the roots, in a liquid form. This food, very much 

 diluted, must be concentrated, and thus assimilated to the 

 plant. We have in the leaves of the plant, a most beauti- 

 ful arrangement to answer this need. They are filled with 

 " stomata," or breathing pores, which allow exhalation when 

 moisture is freely supplied, and check it when the supply 

 falls off. These little mouths are found on both sides of 

 the leaf in most plants, but usually on the lower side in by 

 far the greater number. They vary in different plants from 



