CHAPTER IX 

 THE PLANT AS AFFECTED BY WATER 



The water supply dissolves the food materials in the 

 soil; water is itself used in the growth of the plant; 

 it modifies atmospheric and soil conditions. Its relation 

 to plant culture is therefore very important. 



217. Destruction of roots. — Excessive water in the 

 soil destroys the roots of plants. We saw that oxygen, is 

 necessary to the life of roots (89). When the soil cavities 

 are filled with water, the roots are soon deprived of oxygen, 

 because the little oxygen contained in the water is soon 

 exhausted (93). Smothering and decay of the roots fol- 

 low. Seeds planted under such conditions usually fail. 

 The soil water that is most useful to land plants is that 

 which remains attached to the soil particles after percola- 

 tion has nearly ceased (capillary water). Such water is 

 well aerated because it is interspersed with cavities that 

 are filled with air (91). 



In the open ground the remedy for excessive soil water 

 may usually be found in underground drainage. But the 

 same trouble often occurs in potted plants, as the result of 

 too compact soil or too copious watering. The expert 

 recognizes this condition by a sour odor of the soil, by 

 lifting the pot, or by tapping the pot with his knuckle. If 

 the soil is soggy, the weight will betray the fact, or the 

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