CHAPTER II. 



OF THE MOISTURE OF THE SOIL.— WATERING. 



It has already been shown that water is one of the most 

 important ingredients in the food of plants, partly from their 

 having the power of decomposing it, and partly because it is the 

 vehicle through which the soluble matters found in the earth 

 are conveyed 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, contains 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 congenial 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 

 moisture is required by plants with perennial stems, even in 

 their season of rest, because it is necessary that their system 

 should, at that time, be replenished with food against the 

 renewal of active vegetation. Hence, when trees are taken out 

 of the earth in autumn, and allowed to remain exposed to a dry 

 air all the winter, they either perish, or are greatly enfeebled. 

 If, on the other hand, the soil in which they stand is filled with 

 moisture, their system is distended with aqueous matter at a time 

 when it cannot be decomposed or thrown off, and the plant either 



