134 PRINCIPLES OF PLANT CULTURE 



matters, causing their premature death (125), and favors 

 the development of certain fungous parasites. The ef- 

 fects of insufScient moisture in the air are often very 

 noticeable upon plants kept in living-rooms in winter. 

 Such plants, especially when few in niunber, rarely make 

 satisfactory 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. 



InsufScient moisture in the open air rarely occurs unless 

 there is also a dearth of water in the soil. 



228. Retarding growth. — 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. Hastening maturity. — Drought tends to hasten 

 maturity, especially in annual plants, since it favors 

 flowering (134). Lettuce, spinach, rhubarb and the 

 like " run to seed " earlier if insufficiently supplied with 

 water. Potatoes usually ripen earlier in dry seasons 

 than in wet ones. If the drought is sufficiently severe or 

 sufficiently prolonged, diminution or failure of seedage 

 results. 



230. Toughness of plant tissues results from drought. 

 The crispness and tenderness that give quality to salad 

 vegetables, as celery, lettuce, radish and the like, due 

 to a distended condition of their cell-walls, is largely 



