OX THE FOOD OF PLANTS. 117 



does not appear, that the stems were sealed, 

 and therefore they were left with the power of 

 taking up the fluid through the usual and natural 

 channels. 



Sir Humphry Davy again says, " Vegetable 

 " and animal substances deposited in the soil, as 

 " shown by universal experience, are consumed 

 " during the process of vegetation, and they can 

 " only nourish the plant by affording solid matter 

 " capable of being dissolved by the fluids in the 

 " leaves of vegetables : but such parts of them 

 " as are rendered gaseous, and that pass into the 

 " atmosphere, must possess a comparative small 

 " effect, for gases soon become diffused through 

 " the mass of the surrounding air." 



" The great object in the application of ma- 

 " nures, should be to make it afford as much 

 " soluble matter as possible to the roots of the 

 " plant, and that in a slow and gradual manner, 

 " so that it may be entirely consumed in forming 

 " its sap and organised parts." 



And again, " No substance is more necessary 

 " to plants than carbonaceous matter, and if this 

 " cannot be introduced into the organs of plants, 

 " except in a state of solution, there is every 

 "reason to suppose that other substances less 

 " essential will be in the same case. I found by 

 " some experiments made in 1804, that plants 



i 3 



