116 CHYMISTRY APPLIED TO AGRICULTURE; 



than that of water : not only does it contribute to the 

 nourishment of the plant by its decomposition, which de- 

 posits in the vessels its elementary principles ; but it acts 

 still farther by promoting the fermentation of manures, 

 and by conveying into the vegetable organs the juices 

 and salts. Independently of these properties, water di- 

 lutes the sap, which has become thickened in the body of 

 the plant, and facilitates its circulation ; and likewise fur- 

 nishes abundantly the means of transpiration. The soil is 

 also softened by water, and thus rendered more permeable 

 by the roots, and by atmospheric air which supplies them 

 with the moisture it contains. 



All the excess of water absorbed by plants, is thrown 

 off by transpiration ; and this transpiration is always more 

 or less abundant in proportion to the quantity imbibed. 



The custom of inundating meadows during winter, pre- 

 serves them from the effects of hard frosts. Davy ascer- 

 tained the temperature beneath the bed of ice covering a 

 meadow, and above it: beneath the ice his thermometer 

 stood at 43° ; above the ice at 29°. Every one must have 

 observed, that when the surface of a meadow is only par- 

 tially covered by water during the winter, the herbage 

 upon that part which is left dry, is withered and nearly 

 dead, whilst the rest retains its green hue, and continues 

 to grow. 



The character of water used for irrigation, is a thing of 

 some consequence; that of a living stream is the bes* 

 especially i^ it have, by a long course, become impregnated 

 with a gopa quantity of atmospheric air. 



Though water is the most active agent in vegetation, it 

 is nevertheless necessary to apply it with reserve and cau- 

 tion : the worst effects are produced by irrigating land so 

 often as to keep the soil constantly in the state of a liquid 

 paste. The first evil arising from such a course is that of 

 increasing the size of the plants to the injury of all their 

 other qualities ; for in such a case the fibres of plants be- 

 come loose ; the texture soft and watery ; the flowers are 

 inodorous, and the fruits without firmness, taste, or perfume. 

 The second is, that all useful plants which do not require 

 much water, give place to rushes and flags, which change 

 and ruin the soil : in this case the same evil is produced 

 which we seek to destroy_ in wet lands by the use of soot, 

 gravel, ashes, and other absorbing and saline bodies. 



Frequent irrigations are not injurious to poor, light, 



