SAf/TS. 45 



From this last experiment, as well as from the great 

 proportion in which it exists in the living plant, it evi- 

 dently follows that extract constitutes a vegetable food. 



4. SALTS.— Most plants are found by analysis to 

 contain a certain proportion of salts ; such as nitre and 

 muriate of soda or common salt. How do they acquire 

 them ? In the earlier periods of phytological investiga- 

 tion, when every effect was attributed to the agency of 

 the vital principle as exerted upon the air and water, 

 which the plant inhales or absorbs, it was thought that 

 the salts contained in vegetables are formed in the pro- 

 cess of vegetation ; but this is also one of those extrav- 

 agant conjectures of which further research has expos- 

 ed the absurdity. The salts which have been detected 

 in vegetables are known to exist in the soil. It is most 

 likely therefore that the root absorbs them in solution 

 with the water by which the plant is nourished. For 

 the fact is already ascertained that plants are capable 

 of taking up salts by the root, at least when presented 

 to them in a state of artificial solution ; and if so, there 

 is then reason to presume that they are also taken up 

 by the roots of plants vegetating even in their natural 

 habitations. 



But if salts are thus taken up by the root of the veg- 

 etating plant, does it appear that they are taken up as 

 food ? Some plants, it must be confessed, are injured 

 by the application of salts, as is evident by the experi- 

 ments of Saussure ; but others are as evidently bene- 

 fitted by it. Clover and Lucern have their growth 

 much accelerated by the application of gypsum, though 

 many other plants are not at all influenced by its action. 

 The Nettle, and Borage will not thrive except in such 

 «toils as contain nitre : and plants inhabiting the sea 



