10 ON THE FOOD OF PLANTS. 



passed info its original elements, is fitted for becoming the sup- 

 port of other organized beings. 



In these respects plants bear a close analogy to animals ; like 

 them too, they are possessed of that inconceivable power, by 

 which means they are enabled to assimulate, or change into their 

 substance, a variety of extraneous matter. In common with ani- 

 mals, they have the power of increasing their species : and many 

 of them possess spontaneous motion, or irritability. Indeed, 

 the lowest link in the chain of vegetable beings, approaches so 

 closely to that which holds the same in the animal kingdom, 

 that a well defined line of demarkation has in vain been sought 

 for. 



It has occupied the attention of philosophers for a long period 

 to discover the real nature of the food of plants, nor to this day 

 is the problem satisfactorily solved. It would, however, lead me 

 far beyond the limits which I have proposed to myself in this out- 

 line to notice the conflicting opinions of those who have investi- 

 gated this difficult subject ; let it suffice to observe, that the 

 most generally received is, that water, together with carbon, (the 

 base of charcoal,) either in solution, or combined with an acid 

 gas, constitute the principal food of vegetables ; and that the 

 application of manure, consisting of decaying vegetable and ani- 

 mal matter, to the soil, is the only means within our power, of 

 supplying the plant with the' latter of these essential principles. 



The earths, which are only finely divided flint, limestone, alu- 

 minc, or earth formed from clayslate and analogous rocks, and a 

 few others of less common occurrence, do not constitute any por- 

 tion of the food of plants, the use of them being merely to afford 

 a medium in which the proper food should be administered ; and 

 their fitness for the purpose, depends both on the proportion in 

 which they are combined, and the state of division which they 

 have attained. Thus, a soil is composed principally of silex, 

 that is, earth of flints, particularly if some portion of it be not in 

 a state of minute division, will not be sufficiently compact to re- 

 tain for any length of time, a proper degree of moisture. A soil 

 consisting of nineteen parts out of twenty of siliceous sand, has 

 been found to be perfectly barren, yet so small a portion of finely 

 divided matter, as one part in twelve, it is asserted, is sufficient 

 to adapt it to cultivation. The qualities whereby this sand ma} r 

 be recognised, are, that it docs not effervesce in acids, that it is 



