220 OPEN AIK GRAPE CULTURE. 



growing, the vigor wliicli it communicates to them 

 must also be communicated to the leaves ; but when 

 leaves are growing unusually fast, there is sometimes 

 a danger that they may rob the branches of the sap 

 required for the nutrition of the fruit; and if that 

 happens, the latter falls off. There, then, is a source 

 of danger which must not be lost sight of. No doubt 

 the proper time for using liquid manure is when the 

 fruit is beginning to swell, and lias acquired, by its 

 own green, surface, a power of suction capable of 

 opposing that of the leaves. 



"At that time liquid manure may be applied freely, 

 and continued from time to time as long as the fruit 

 is growing. But at the first sign of ripening, or even 

 earlier, it should be wholly withheld." 



The action of manure is even now very far from 

 being thoroughly understood. When modern chem- 

 istry was first applied to agriculture, it was supposed 

 that the great object of manure was merely to afford 

 food for plants. But it was afterward found that 

 other conditions were of equal importance, and that 

 the advantage of many manures arose from their me- 

 chanical influence upon the soil. At Lois "Weedon 

 in England, excellent cropg of wheat have been raised 

 by thorough cultivation, without the application of 

 manure, and the same principle was advocated by 

 Jethro Tull in 1731, whose famous system of horse 



