Review of ChaptaVs Chemistry of Agriculture. 29 



total darkness. I was much struck, in passing through this gallery, with 

 the different appearances presented by the mushrooms in the various de- 

 grees of light ; those at the entrance were yellow, and their texture so 

 compact that they could hardly be broken by the hand. As I advanced, 

 the reddish yellow color grew gradually fainter, and the texture of the 

 plants more soft and spongy, till at the bottom of the gallery, where a 

 ray of daylight never penetrates, I found the mushrooms, though as 

 large as those at the entrance, perfectly white, and nearly without con- 

 sistency, so much so, that upon pressing them with the hand, they were 

 found to yield much liquid, and hut little fibrous matter. I filled several 

 bottles with these, and took in my hands some of those from the middle 

 and entrance of the gallery. A comparative analysis of these various 

 portions afforded me, from those which grew at the bottom of the gal- 

 lery, only water saturated with carbonic acid, a small quantity of mucil- 

 age, and a little parenchymous fibre swimming in the liquid. The pro- 

 portion of acid was much less, and that of ligneous fibre more consider- 

 able, in the mushrooms plucked from the middle and entrance of the 

 gallery, particularly in the last. Those tVom the dark part of the gal- 

 lery contained only the elements of nutrition not elaborated ; whilst 

 in the other, the process of assimilation was carried on more or less per- 

 fectly, in proportion as light and atmosphreic air had access to them to 

 facilitate vegetation ; otherwise, as carbonic acid was most abundant in 

 those plants which grew in darkness, their texture ought to have been 

 the most thoroughly impregnated with it." 



On the succession of crops, as superseding the old custom 

 of suffering ground to lie fallow, in order to renovate it, 

 we are told, 



" A good system of cropping is the best guarantee of success that the 

 farmer can have ; without this, all is vague, uncertain and hazardous. 

 In order to establish this good system of cropping, a degree of knowledge 

 is necessary, which unhappily is wanting to the greater part of our prac- 

 tical farmers. 1 shall here state certain facts and principles, which may 

 serve as guides in this important branch of agriculture." 



Principle 1. AJl plants exhaust the soil. 



" 2. All plants do not exhaust the soil equally. 



" 3. Plants of different kinds do not exhaust the 



soil in the same manner. 

 *' 4. All plants do not restore to the soil either the 



same quantity or the same quality of ma- 

 nure. 

 " 5. All plants do not suffer weeds to fill the soil 



equally. 

 From such principles carried into detail, the author lays 

 down the following conclusions : 



" 1st. That however well prepared a soil may be, it cannot nourish 

 a long succession of crops without becoming exhausted. 



" 2d. Each harvest impoverishes the soil to a certain extent, depend- 

 ing upon the degree of nourishment which it restores to the earth. 



" 3d. The cultivation of spindle roots ought to succeed that of running 

 and superficial roots. 



" 4th. It is necessary to avoid returning too soon to the cultivation of 

 the same or of analogous kinds of vegetables, in the same soil. 



" 5th. It is very unwise to allow two kinds of plants, which admit of 

 the ready growth of weeds among them, to be raised in succession. 



