PT. III. OR POISONED BY VEGETABLE GROWTH? 139 



absorbed from the soil, since they actually are soil. In 

 trees their quantity, as compared with the combustible 

 parts, is small ; though during the life of the tree, in 

 the chemical processes of decomposition, elaboration, 

 and assimilation, their effects may be very great. The 

 combustible or organic parts of trees, though they are 

 not soil, are absorbed by the roots from the soil ; that 

 is, their constituents are elaborated or chemically pre- 

 pared for the plant in the soil, and absorbed by the 

 roots from the soil. But as neither animals nor plants 

 bring anything into the world with them, so neither of 

 them take anything away with them ; and if their 

 remains are restored to the soil, no impoverishment will 

 take place. 



I have no faith in the supposed excretion from the Roots do 



not excrete. 



roots of substances unnecessary to the growth of the 

 tree. If this were so, the roots would soon be sur- 

 rounded with such substances, and w^ould be incapable 

 of absorbing nutriment. In chalk districts eternal 

 woods are found composed of nothing but beech ; in 

 other soils, of nothing but oak. The oldest vineyards 

 and the oldest hop-gardens are the best. And how 

 many milhons of acres are in this world covered with 

 perpetual heath ! In all these cases, if the roots 

 excreted substances unfit for nourishing the plants, the 

 whole soil would have become saturated with them. 

 Land plants grown in water are always unhealthy. 

 Under these circumstances, may not colouring matter, 

 or other substances supposed by Macaii'e-Princep to be 



