66 FOOD OF THE VEGETATING PLANT. CHAP. I. 



be supposed to enter it by the root : but these sub- 

 stances may certainly contain vegetable nourish- 

 ment ; and they will perhaps be found to be taken 

 up by the plant in proportion to their degree of 

 solubility in water and to the quantity in which 

 they exist in the soil. Now one of the most im- 

 portant of these substances is vegetable extract. 

 As a com- When plants have attained to the maturity of 

 part of their species, the principles of decay begin gradually 

 mould ble to operate upon them, till they at length die and are 

 converted into the dust from which they sprang, thu& 

 resembling the animal to whom they afford support. 

 The substance to which they are finally converted 

 has been denominated vegetable mould. And this, 

 as might be expected, constitutes a considerable 

 proportion of the soil. The chance then is, that it 

 , is again converted into vegetable nourishment, and 

 Is soluble again enters the plant. But it cannot wholly enter 

 andhence the plant because it is not wholly soluble in water. 

 by S the able ^ art ^ lt > however, is soluble and consequently 

 root. capable of being absorbed by the root, and that is the 

 substance which has been denominated extract. 



Saussure filled a large vessel with pure mould of 

 turf, and moistened it with distilled or rain water 

 till k was saturated. At the end of .five days, when 

 it was subjected to the action of the press, 10,000 

 parts in weight of the expressed and filtered fluid 

 yielded by evaporation to dryness 20 parts of extract. 

 In a similar experiment upon the mould of a kitchea- 

 garden which had been manured with dung, 10,000 



