140 EUROPEAN AGRICULTURE. 



and in which it is continually renewed. If it was the water 

 alone, which produced this effect, marshy meadows should be 

 most fertile. Hence it is not sufficient, in irrigating meadows, to 

 convert them into marshes, by covering, for several months, their 

 surface with water, which is not renewed ; for the advantage of 

 irrigation consists principally in supplying oxygen to the roots 

 of plants. The quantity of water necessary for this purpose is 

 very small, so that it is sufficient to cover the meadow with a 

 very thin layer, if this be frequently renewed.&quot;* 



These are the opinions entertained by different eminent in 

 dividuals on the subject of irrigation. They cannot be said to 

 contradict each other ; but whether or not they reach the whole 

 of the case, must be left to the judgment of my reader. The 

 beneficial and productive influences of this process in an agricul 

 tural view are perfectly established. Any person may perceive it 

 at the breaking up of the spring, when the snow water is turned 

 into a restricted channel down a bank, that there the verdure 

 and the growth of the grass will sometimes exhibit a month s 

 advance over other parts of the field. Every one perceives 

 its effects, when a drought is followed by a copious rain, and the 

 whole aspect of the fields is immediately changed. Whatever 

 may be the theory, which we deem most reasonable, in respect 

 to the operation of water upon vegetation, it is enough for all 

 practical purposes to know the fact ; and the knowledge of this 

 fact, and the practice founded upon it, are almost coincident with 

 the art of cultivation. The amounts of the annual and fertil 

 izing inundations of the Nile, arid the plans for watering the 

 fields after the dry season has commenced, must be well known 

 to my readers. The productive influences of the overflowing 

 of several of our great rivers upon their bottom and alluvial 

 lands, are perfectly understood by the agricultural community. 

 These, however, are usually charged with an enriching deposit, 

 which is often made in considerable quantities, and the effects 

 of which are always remarkable. 



2. GENERAL PRINCIPLES AND DIRECTIONS FOR IRRIGATION. 

 Some points respecting irrigation may be considered as well 

 established, to which it is proper that I should refer. It is set- 



* Liebig s Agricultural Chemistry, p. 168. 



