NATURE AND SOURCES OF FOOD. 95 



accumulate iron so that on decaying they leave a sediment of 

 iron rust in the water ; chlorine is found in all marine plants ; 

 phosphorus in the onion ; and sulphur in mustard seed, in 

 celery, and in ginger. The immense quantities of water vari- 

 ously impregnated with these foreign bodies, which pass 

 through a plant, being condensed by evaporation in the leaves, 

 is sufficient to account for their presence, in appreciable 

 quantities in the plant, however minute may be their propor- 

 tion in the water which the roots imbibe. Hence it is found 

 that plants will not grow in distilled water, or water freed from 

 all foreign ingredients ; and also that the water exhaled by 

 plants is so pure that not a trace of foreign matter is discover- 

 able in it ; the stomata or pores of the leaves are in fact the 

 most perfect stills in the great laboratory of nature. About 

 two-thirds of the fluid taken up by the spongioles of the roots, 

 is evaporated from the leaves of plants in the form of water, 

 and consequently about one-third remains in the plant in a 

 highly concentrated state, and contains the carbonic acid and 

 other earthy ingredients which happen to be dissolved in the 

 fluid when first presented to the roots. - 



Although the ash or inorganic matter in plants constitutes a 

 very small proportion of their substance, yet its importance is 

 not on this account to be underrated. The small per centage 

 of inorganic matter contained in them appears to be absolutely 

 necessary to their healthy growth. It is for this reason that 

 the soil exercises such a marked influence on the distribution 

 of species. It is impossible to examine the plants which spring 

 up spontaneously in any district, without arriving at the conclu- 

 sion that they are influenced in the development of the pecu- 

 liarities of their organization, by certain inorganic matters which 

 abound in the soils in which they grow. The barren mountain 



