Plants as Affected by Excessive Water. 137 



Section III. The Plant as Affected by Unfavor- 

 able Water Supply. 



A — ^By Excessive Water. 



217. 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 ex- 

 hausted (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 

 percolation 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 sound given out by the pot will be that 

 of a compact mass instead of a more or less hollow 

 body, as is the case with a pot of well-aerated soil. To 

 remedy the evil, repot the plant in fresh soil of a proper 

 condition of moisture, providing abundant drainage at 

 the bottom of the pot (412). 



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