A NEW TONIC FOR THE PEAR TREE. 



pacity for taking up and digesting this sub- 

 stance. 



Now the carbon, which is the food of 

 plants, is not found or taken up by them in 

 a free or simple state, but in the form of 

 carbonic acid — that is, carbon combined with 

 oxygen. This carbonic acid abounds in the 

 air, which is the food of plants taken up by 

 their leaves ; and in the water, containing 

 solutions of rich soils, which is taken up by 

 their roots. According to Liebig, much the 

 largest portion of the carbonic acid, which 

 forms the food of plants, is absorbed by the 

 surface of the leaves. 



But as carbon, and not carbonic acid, is 

 the food of plants, it is evident that the lat- 

 ter must have the power of decomposing car- 

 bonic acid, so as to leave them in possession 

 of the carbon, and also of expelling the su- 

 perfluous oxygen. 



This admirable power is possessed by the 

 leaves of plants in a manner somewhat ana- 

 lagous to that belonging to the lungs of ani- 

 mals. Carbonic acid, in the form of gas, is 

 absorbed by the green leaves of a growing 

 plant, and is exposed by them to the action 

 of the sun's light; and the oxygen is then, 

 by the force of the vital power, separated 

 from the carbonic acid, and given out by 

 the leaves, while the carbon which remains 

 enters into the system of the tree or plants, 

 and immediately increases its bulk. 



Upon the rapidity with which this decom- 

 position or digestion of carbonic acid goes 

 on, must, of course, depend the vigor and 

 growth of the tree. It is not only necessa- 

 ry to its action that the leaves of plants 

 should be exposed to the light, but that they 

 should be green. Plants grown in the dark 

 are always not only comparatively feeble, 

 and destitute of strength and substance, but 

 they are also colourless. This is owing to 

 the deficiency in carbon, from the want 

 of the sun's light to assist in separating 



it from the carbonic acid which they ab- 

 sorb. 



A diseased or sickly state of plants, also 

 immediately arises, if, from any cause, the 

 leaves lose their green colour — for with the 

 green colour is lost, in a great measure, the 

 power of digesting their food, that is, sepa- 

 rating the carbon from the oxygen. 



Now the sulphate of iron used by M. 

 Gris, and the oxides of iron which we re- 

 commend for the pear, both, we conceive, 

 act as a specific in restoring the natural 

 green colour and consequent healthy action 

 of the leaves of plants. 



The bad health of many plants, with yel- 

 low chlorotic foliage, we conceive, arises 

 from the irretention of an excess of oxygen — 

 or from their not being able to expel the 

 oxygen and assimilate the carbon of carbo- 

 nic acid in a natural manner. 



M, Gris has proved that the salts of iron, 

 applied to the surface of sickly yellow 

 leaves, very speedily restores their green 

 colour, and with it the health of the plant. 

 The same result follows, in a less rapid 

 manner, the absorption of the solutions of 

 the salts of iron by the roots. 



We believe, from our own observations, 

 that the same effect is produced on the dis- 

 eased foliage of the pear (and probably 

 other fruit trees) by the application of com- 

 mon iron rust, or oxide of iron in small 

 quantities. Whether the peroxide of iron 

 acts by entering into conibination with the 

 excess of oxygen in pale and sickly foliage, 

 or otherwise specifically upon the vital pow- 

 er of the plant itself, we are not yet able to 

 say. The subject has not been noticed by 

 chemists. Baron Liebig only says, " There 

 are inorganic substances, the total want of 

 which, in animals, is inevitably productive 

 of death. Plants, for the same reason, can- 

 not live unless supplied with certain metal- 

 lic compounds." But though oxide of iron 



