316 



LEAVES AND ROOTS— THEIR FUNCTIONS AND STRUCTURE. 



and combines with the juices already there, 

 while the oxygen is liberated in a free state. 

 Now carbon is the absolutely iiecessary 

 ino-redient required for the growth and sub- 

 stance of plants. It is that, in fact, which 

 forms the lif(,7iin, or greatest portion of the 

 wood, which, when burnt and divested of 

 its extraneous matter, is carbon in its solid 

 state. But we are now speaking of carbon 

 in its paseous form, which however is never 

 formed, and cannot be realized pure, or in 

 a free state ; but always joined with some 

 other gas or substance : thus, while float- 

 ino- in the atmosphere, it is in the form of 

 carbonic acid gas. You are aware that 

 this gas is most noxious and detrimental to 

 animal life, and, but for this wise provision 

 of nature, would accamulate in such quan- 

 tities as to depopulate the world. But Al- 

 mio-hty God, the great ruler of the uni- 

 verse, has ordained that this deleterious 

 compound should be the very food and 

 substance of every tree of the forest, and 

 the grass which clothes the fields. In 

 many of the natural processes of this life, 

 and in decomposition after death, this gas 

 is generated. When we breathe, we in- 

 hale an atmosphere of oxygen and nitro- 

 gen, with a very small proportion, as al- 

 ready stated, of carbonic acid gas ; but we 

 expire an air loaded with it. The act of 

 combustion is to generate carbonic acid 

 gas. Fermentation and decomposition, or 

 putrefaction, all generate this noxious gas. 

 Nay, the generating of this gas exists in 

 the very act, whether of germination, vege- 

 tation, combustion, fermentation, or putre- 

 faction. If, then, this gas, so destructive 

 to the animal economy, is generated in 

 such quantities, that if some means were 

 not at hand to again resolve it into its ele- 

 ments, it would render the globe unin- 

 habitable, it is gratifying to know that 

 those means are at hand, in every leaf 



which is exposed to the surrounding at- 

 mosphere. Light and sunshine are the 

 two great influences which act on vegeta- 

 ble matter, in restoring to a proper state a 

 deteriorated atmosphere ; the former hav- 

 ing the peculiar faculty of giving the green 

 colour to vegetable matter ; and the latter, 

 by its influence on geen vegetable matter, 

 in decomposing carbonic acid gas, — the 

 carbon being retained, and the oxygen set 

 free. You are, of course, aware that oxy- 

 gen is the grand supporter of animal life ; 

 without its aid and application, animal life 

 would quickly become extinct. It is the 

 supporter of combustion ; and its presence 

 is required in the germination of seeds, and 

 the vegetation of plants. 



The leaves, then, are the organs of as- 

 similation. In them the sap, having in 

 solution the inorganic constituents of the 

 plant derived from the soil, and deriving 

 the carbon, which has been retained in the 

 stomata, from the atmosphere, as also its 

 nitrogen, elaborated now into the proper 

 juices of the plant, returns through the de- 

 scending vessels, on the inner side of the 

 bark to the root. 



On the subject of the carbon being de- 

 rived from the atmosphere, Prof. Liebig 

 says — " It is not denied that manure exer- 

 cises an influence upon the development of 

 plants ; but it may be affirmed, with posi- 

 tive certainty, that it neither serves for the 

 production of carbon, nor has any influence 

 upon it, because we find that the quantity 

 of carbon produced by manured lands is 

 not greater than that yielded by lands 

 which are not manured. The discussion 

 as to the manner in which manure acts has 

 nothing to do with the present question, 

 which is, the origin of carbon. The carbon 

 must be derived from other sources ; and 

 as the soil does not yield it, it can only be 

 extracted from the atmosphere." 



