I. AGRICULTURE AND RURAL ECONOMY. 385 



eral dressing of sand, which supplies silica, and of wood-ash- 

 es, which furnish the potash the substance required to make 

 glass Nature will employ those ingredients, to a great ex- 

 tent, in covering the leaves with an elastic glass, and the 

 fruit with a thick, transparent varnish, produced from the 

 silica and potash, which will protect the leaves from blight, 

 and the fruit from rust, scales, and cracks. This fact has been 

 demonstrated repeatedly in some fruit-producing localities, 

 where wood-ashes or coal-ashes have been scattered about 

 pear-trees and apple-trees so liberally that all grass and weeds 

 were destroyed. Flint, sharp sand, and quartz are composed, 

 for the most part, of silica. Hence the propriety of mingling 

 scourino^-sand with the soil in which flowers are cultivated. 

 Divest the soil of all silica and alkali where useful plants and 

 beautiful flowers are to be grown, and not one would attain 

 to perfect development, simply because silica and potash are 

 eminently essential to impart stifi'ness to the stems and elastic- 

 ity and tenacity to the leaves. When grape-vines, for ex- 

 ample, which are growing in a sandy soil, have access to 

 potash in abundance, the leaves will appear as tough as leath- 

 er, and no mildew nor rust will ever afiect the foliage or in- 

 jure the fruit. 17 A, May 1, 1872, 261. 



FUXCTIOX OF ORGANIC SUBSTANCES IN THE SOIL. 



A numl^er of experiments by Grandeau upon the part 

 which organic substances in the soil play in the nutrition of 

 plants led to the following conclusions : 1. In fertile soils 

 the mineral ingredients necessary to the j^lant are present in 

 the form in which stable manure furnishes them. 2. The fer- 

 tility of a soil depends essentially upon the amount of min- 

 eral matter in the organic substances that are soluble in 

 ammonia, the organic matter acting as a vehicle of the min- 

 eral matter. This has suggested the combination of the two 

 as a manure, to be applied directly to such soils as require 

 stimulation. Quite recently an establishment in Paris, which 

 manufactures glue and gelatine on a large scale, and, of 

 course, has a great quantity of bone on hand, has succeeded 

 in manufacturing a compound of this earth with roasted ani- 

 mal refuse, which proves to be extremely efficient for the 

 purpose in question. 18 C, October 16, 1872, 666. 



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