Obsei'vations on Liebi^s " Orgmiic Chemhtry.^^ 105 



of plants are known and furnished. The Gramineae and £qul- 

 setaceae require silicate of potash ; the genus O'xalis, potash ; 

 the Salsola and Salicornia, common salt. Wheat and other 

 grains require phosphate of magnesia. The roots of ^lthse\i 

 contain more phosphate of lime than woody fibre. These are 

 proofs, he says, that all these substances and many others, equally 

 as well as nitrogen and water, are necessary before the plant can 

 be placed in circumstances favourable to its growth. 



On the Origin and Action of Humus. He defines humus to 

 be woody fibre in a state of decay ; and humic acid as a product of 

 the decomposition of humus by alkalies, which does not exist in 

 humus. He also states that woody fibre forms this substance, or 

 humus, by uniting with the oxgyen of the air by a process 

 similar to putrefaction, and for which he has invented the name 

 of Eremacausis, or tardy combustion ; a slow union of oxygen 

 to the woody fibre, which gives off carbonic acid till converted 

 into a brown coaly-looking substance called mould. He de- 

 scribes this humus as existing in soil permeable to the air, 

 surrounded with an atmosphere of its own, of the carbonic acid 

 formed by the absorption of oxygen; this atmosphere around it 

 prevents the further decay of the humus till removed, when a 

 fresh supply of air and oxgyen causes a renewal of carbonic 

 acid. This carbonic acid, he says, is taken up by the fibres of 

 the root, and forms for a time the food of the young plant: 

 these fibres he describes as forming, at the same time, mouth, 

 lungs, and stomach to the plant. It has been customary to 

 compare the actions of plants and animals, and it may sometimes 

 help to convey the meaning of the author, but is inapplicable. 

 The food of animals is taken in by the mouth, digested by 

 the stomach, mixed with the bile, and the nutriment absorbed 

 by the lacteals and conveyed to the blood, which is aerated in 

 the lungs. Were we to liken the fibres to mouth, and the 

 leaves to stomach, where are the lungs, and the circulation re- 

 turning to be aerated ? Jf we say the leaves act both as stomach 

 and lungs, this is a twofold action of which we have no parallel in 

 the animal economy. Perhaps to assume the earth as stomach, 

 the fibres as mouth, and the leaves as lungs, might be nearest 

 the mark; but bolh order and action are different, and the 

 comparison is, perhaps, of little use. But to return to our 

 subject, the fibres, he says, perform all these offices, till ma- 

 turity; which he defines as the time when the organs are fit to 

 provide food for themselves from the atmosphere, by the leaves 

 absorbing carbonic acid and dew. Further on he says, a plant 

 gains another mouth and stomach with every new fibre of the 

 root, and every new leaf; and, therefore, we are left to con- 

 jecture for ourselves, what is the cause of the new fibres, formed 

 newly every year, ever losing their power of absorption ; we 



