240 GREEN AND DKY CROPS. 



of it, together with all the organic matter the plant itself has 

 elaborated, from oxygen and hydrogen, carbon, and nitrogen, 

 from whatever source derived. It has decomposed, during 

 the short period of its growth, as has been already pointed 

 out, more silicates and salts than the air only could effect 

 during the same period, which, being turned in, restore to 

 the soil from which they grew, salts and silicates in a new 

 form, whose action on vegetation is like that of alkalies. 

 But, powerful as are the effects of green crops, ploughed in, 

 it is the experience of some practical men, that one crop 

 allowed to perfect itself and die where it grew, and then 

 turned in dry, is superior to three turned in green. The 

 whole result is explained by the fact, that dry plants give 

 more geine than green. Green plants ferment, dry plants 

 decay. A larger portion escapes in fermentation, as gas and 

 more volatile products are formed, than during decay. The 

 one is a quick consuming fii-e, the other a slow mouldering 

 ember, giving off, during all its progress, gases, which feed 

 plants, and decompose the silicates of soil. 



289. The power of fertility which exists in the silicates o? 

 soil is unlimited. An improved agriculture must depend 

 upon the skill with which this power is brought into action. 

 It can be done only by the conjunction of salts, geine, and 

 plants. Barren sands are worthless, a peat bog is little bet- 

 ter; but a practical illustration of the principles which have 

 been maintained, is afforded by every sandy knoll made fer- 

 tile by spreading swamp muck upon it. This is giving geine 

 to silicates. The very act of exposure of this swamp muck, 

 has caused an evolution of carbonic acid gas ; that decom- 

 poses the silic4ites of potash in the sand ; that potash converts 

 the insoluble into soluble manure, and lo ! a crop. That 

 growing crop adds its power to the geine. If all the long 

 series of experiments under Von Voght, in Germany, are to 



