142 Principles of Plant Culture. 



B THE PL.ANT AS AFFECTED BY INSUFFICIENT WATER. 



227. Insufficient Moisture in the Air Causes Ex- 

 cessive Transpiration (74), which reduces the tension 

 of the cell-walls and thus retards growth (62). It also 

 tends to clog the leaves with useless mineral matters, 

 causing their premature death (125), and favors the 

 development of certain fungous parasites. The effects 

 of insufficient moisture in the air are often very notice- 

 able upon plants kept in living-rooms in winter. Such 

 plants, especially when few in number, rarely make sat- 

 isfactory growth and the lower leaves continually per- 

 ish. Moistening the air by evaporating water in the 

 room, or setting the pots containing the plants upon a 

 table covered with moist sand usually remedies the 

 trouble. 



Insufficient moisture in the open air rarely occurs 

 unless there is also a dearth of water in the soil. 



228. Insufficient Moisture in the Soil Retards 

 Growth both by reducing the tension of the cell-walls 

 (62), and by lessening the supply of food from the soil. 

 The tendency of drought is, therefore, to starve the 

 plant. 



Plants that have been subject to insufficient water 

 from the beginning usually suffer less from drought 

 than those previously well watered, because their root 

 system has become more extensively developed (111). 



229. Drought tends to Hasten Maturity, especially 

 in annual plants, since it favors flowering (134). Let- 

 tuce, spinach, rhubarb, etc., "run to seed" earlier if 

 insufficiently supplied with water. Potatoes usually 



