OF THE MOISTURE OF THE SOIL, 113 



CHAPTEE II. 

 OP THE MOISTURE OP THE SOIL.— WATERING. 



It has already (38) been shown that water is one 

 of the most important elements in the food of 

 plants, partly from their having the power of decom- 

 posing it, and partly because it is the vehicle through 

 which the soluble matters found in the earth are con- 

 veyed into the general system of vegetation. Its 

 importance depends, however, essentially upon its 

 quantity. 



We know, on the one hand, that plants will not 

 live in soil which, without being chemically dry, con- 

 tains so little moisture as to appear dry ; and, on the 

 other hand, an excessive quantity of moisture, is 

 in many cases, equally prejudicial. The great points 

 to determine are, the amount which is most conge- 

 nial to a given species under given circumstances, 

 and the periods of growth when water should be 

 applied or withheld. 



When a plant is at rest, that is to say, in the winter 

 of northern countries and the dry season of the 

 tropics, but a small supply of water is required by 

 the soil, because at that time the stems lose but little 

 by perspiration, and consequently the roots demand 

 but little food ; nevertheless, some terrestrial mois- 

 ture is required by plants with perennial stems, even 

 in their season of rest, because 34) it is necessary 

 that their system should, at that time, be replenished 



