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CHAPTER IX. 



OF THE FOOD OF PLANTS MANURE. 



The principal part of the food of plants is derived from the 

 earth, and is introduced into their system through the roots. 

 The latter are, however, incapable of absorbing anything 

 soHd ; fluid and gaseous matter only can pass through their 

 spongelets. It is, perhaps, exclusively in the form of water 

 that the nutritive matter of the soil is received by roots ; not, 

 however, of pure water, which in fact does not exist in nature, 

 but of water holding: various solid matters in solution, the 

 most remarkable and abundant of which are silex, lime, and 

 many of its salts, several other earths, oxyde of iron, and 

 copper. 



These substances, however, although the}' undoubtedly each 

 perform their allotted part in the economy of vegetation, — 

 consolidating the tissue, hardening the cuticle, or assisting 

 in depriving a plant of organs which become unhealthy and 

 worn out, — cannot be altogether considered as nutritive mat- 

 ter. There are, perhaps, only two formes of matter, which can 

 properly be called nutritive ; the one is carbon, the other water. 



Soil in its natural state is filled with the remains of organic 

 bodies, which decompose and become converted into carbo- 

 nic acid. In proportion to the abundance of these is soil 

 fertile. Tlie carbonic acid, thus incessantly forminor below 

 the surface of the earth, enters freely into the roots ; combining 

 with water and such other principles as may already have 

 been formed there, it ascends the stem, appai-ently decompos- 

 ing to a certain extent as it passes along, and giving its oxygen 

 to the spiral vessels, which convey it into other parts of the 

 system; when it reaches the leaves, it liberates its oxygen 

 completely, and leaves its carbon to combine with the 

 tissue of vegetation, or to enter into new proportions with 



X 



