FOOD OF PLANTS. 17 



and evidently derived little or no sustenance 

 from the water with which they were supplied. 

 Experiments of a similar nature were made by 

 Bonnet, and with the like result. When plants 

 are contained in closed vessels, and regularly 

 supplied with water, but denied all access to 

 carbonic acid gas, they are developed only to a 

 very limited extent, determined by the store of 

 nutritious matter which had been already col- 

 lected in each plant when the experiment com- 

 menced, and which, by combining with the 

 water, may have afforded a temporary supply of 

 nourishment. 



But the water which nature furnishes to the 

 vegetable organs is never perfectly pure ; for, be- 

 sides containing air, in which there is constantly 

 a certain proportion of carbonic acid gas, it has 

 always acquired, by percolation through the soil, 

 various earthy and saline particles, together with 

 materials derived from decayed vegetable or 

 animal remains. Most of these substances are 

 soluble, in however minute a quantity, in water: 

 and others, finely pulverized, may be suspended 

 in that fluid, and carried along with it into the 

 vegetable system. It does not appear, however, 

 that pure carbon is ever admitted ; for Sir H. 

 Davy, on mixing charcoal, ground to an im- 

 palpable powder, with the water into which the 

 roots of mint were immersed, could not discover 

 that the smallest quantity of that substance had 



VOL. II. c 



