BARK VIEWED AS EXCREMENTITIOUS 1A5 



There is every reason to believe that this separation takes place 

 over the whole surface ; it is observed not only on the stem, but 

 also on the smallest twigs ; and hence we must conclude that the 

 same excretory process goes on in the roots. 



When a branch of a willow is allowed to vegetate in rain-water, 

 the latter assumes gradually a dark-brown color. The same 

 phenomenon is observed in bulbous plants (such as hyacinths) 

 allowed to grow in pure water. It therefore cannot be denied 

 that excrements are actually separated by plants, although it is 

 very possible that they do not all separate them in the same 

 degree. 



It is generally admitted by farmers, as the result of experience, 

 that a soil is enriched in organic matters by the culture cf peren- 

 nial plants, such as sainfoin and lucerne, which are distinguished 

 for the extensive ramification of their roots and strong growth of 

 their leaves ; the cause of their enriching power will perhaps be 

 explained from the above remarks. 



We cannot effect the formation of ammonia on our cultivated 

 land, but it is in our power to obtain an artificial production of 

 humUs: this must be viewed as one of the objects of a system of 

 rotation, and as a second cause of the advantage arising from it. 



By sowing a field with a fallow crop, such as clover, rye, 

 lupins, buck- wheat, &c, and by ploughing and incorporating with 

 the soil, the plants, when they have nearly come to blossom, we 

 procure to the young plants of a new crop sown on the field a 

 maximum of nourishment and an atmosphere of carbonic acid, in 

 consequence of the decay of the preceding crops. All the nitro- 

 gen drawn from the atmosphere by the preceding plants, and all 

 the alkalies and phosphates received from the soil, now serve to 

 cause a luxuriant growth to the plants which succeed. 



