132 Principles of Plant Culture. 
rooms in winter. Such plants, especially when few in num- 
ber, rarely make satisfactory growth and the lower leaves 
continually perish. Moistening the air by evaporating water 
in the room, or setting the pots containing the plants upon 
a table, covered with sand that is kept moist, usually rem- 
edies the trouble. 
Insufficient moisture in the open air rarely occurs unless 
there is also a dearth of water in the soil. 
229. Insufficient Moisture in the Soil Retards 
Growth both by reducing the tension of the cell-walls (63), 
and by lessening the supply of food from the soil. The 
tendency of drought is, therefore, to starve the plant. 
A moderate degree of drought probably tends to promote 
flowering by restricting growth (135 B), but if the drought 
is sufficiently severe, or sufficiently prolonged, diminution 
or failure of seedage results. 
Plants that have been subjected to insufficient water sup- 
ply from the beginning usually suffer less from drought 
than those previously well supplied with water, because 
their root system has become more extensively developed 
(112). 
230. Drought tends to Hasten Maturity, especially 
in annual plants, since it favors flowering (135). Lettuce, 
spinach, rhubarb etc., ‘run to seed” earlier if insufficiently 
supplied with water. Potatoes usually ripen earlier, and 
yield less, in dry than in wet seasons. 
231. Toughness of Plant Tissues Results from 
Drought. The crispness and tenderness that give quality 
to salad vegetables, as celery, lettuce, radish etc., due to a 
distended condition of their cell-walls, is largely wanting 
when the water supply during growth has been insuflicient. 
