AGRICULTURAL CHEMISTRY. 



the organs by which it obtains food from 

 the atmosphere are formed, the carbonic acid 

 of the soil is no farther required. 



Deficiency of moisture in the soil, or its 

 complete dryness, does not now check the 

 growth of a plant, provided it receives from 

 the dew and the atmosphere as much as is 

 requisite for the process of assimilation. 

 During the heat of summer it derives its 

 carbon exclusively from the atmosphere. 



We do not know what height and strength 

 nature has allotted to plants; we are ac- 

 quainted only with the size which they 

 usually attain. Oaks are shown, both in 

 London and Amsterdam, as remarkable 

 curiosities, which have been reared by Chi- 

 nese gardeners, and are only one foot and a 

 half in height, although their trunks, barks, 

 leaves, branches, and whole habitus, evince 

 a venerable age. The small parsnep grown 

 at Teltow,* when placed in a soil which 

 yields as much nourishment as it can take 

 up, increases to several pounds in weight. 



The size of a plant is proportional to the 

 surface of the organs which are destined to 

 convey food to it. A plant gains another 

 mouth and stomach with every new fibre 

 of root, and every new leaf. 



The power which roots possess of taking 

 up nourishment does not cease as long as 

 nutriment is present. When the food of a 

 plant is in greater quantity than its organs 

 r -quire for their own perfect development, 

 tiit superfluous nutriment is not returned to 

 the soil, but is employed in the formation of 

 new organs. At the side of a cell, already 

 formed, another cell arises ; at the side of a 

 twig and leaf, a new twig and a new leaf 

 are developed. These new parts could not 

 have been formed had there not been an 

 excess of nourishment. The sugar and 

 mucilage produced in the seeds, form the 

 nutriment of the young plants, and disap- 

 pear during the development of the buds, 

 green sprouts, and leaves. 



The power of absorbing nutriment from 

 the atmosphere, with which the leaves of 

 plants are endowed, being proportionate to 

 the extent of their surface, every increase 

 in the size and number of these parts is ne- 

 cessarily attended with an increase of nutri- 

 tive power, and a consequent farther de- 

 velopment of new leaves and branches. 

 Leaves, twigs, and branches, when com- 

 pletely matured, as they do not become 

 larger, do not need food for their support. 

 For their existence as organs, they require 

 only the means necessary for the perform- 

 ance of the special functions to which they 

 are destined by nature; they do not exist on 

 their own account. 



We know that the functions of the leaves 

 and other green parts of plants are to absorb 

 carbonic acid, and with the aid of light and 



* Teltow is a village near Berlin, where small 

 parsneps are cultivated in a sandy soil ; they are 

 nuch esteemed, and weigh rarely above one 

 t unce. 



moisture, to appropriate its carbon. These 

 processes are continually in operation ; they 

 commence with the first formation of the 

 leaves, and do not cease with their perfect 

 development. But the new products arising 

 from this continued assimilation are no 

 longer employed by the perfect leaves in 

 their own increase : they serve for the for- 

 mation of woody fibre, and all the solid 

 matters of similar composition. The leaves 

 now produce sugar, amylin or starch, and 

 acids, which were previously formed by the 

 roots when they were necessary for the de^ 

 velopment of the stem, buds, leaves, and 

 branches of the plant. 



The organs of assimilation, at this period 

 of their life, receive more nourishment from 

 the atmosphere than they employ in their 

 own sustenance ; and when the formation 

 of the woody substance has advanced to a 

 certain extent, the expenditure of the nutri- 

 ment, the supply of which still remains the 

 same, takes a new direction, and blossoms 

 are produced. The functions of the leaves 

 of most plants cease upon the ripening of 

 their fruit, because the products of their 

 action are no longer needed. They now 

 yield to the chemical influence of the oxygen 

 of the air, generally suffer a change in 

 colour, and fall off. 



A peculiar "transformation" of the mat- 

 ters contained in all plants takes place in the 

 period between blossoming and the ripening 

 of the fruit; new compounds are produced, 

 which furnish constituents of the blossoms, 

 fruit, and seed. An organic chemical 

 "transformation" is the separation of the 

 elements of one or several combinations, 

 and their re-union into two or several others, 

 which contain the same number of elements, 

 either grouped in another manner, or in dif- 

 ferent proportions. Of two compounds 

 formed in consequence of such a change, 

 one remains as a component part of the 

 blossom or fruit, while the other is separated 

 by the roots in the form of excrementitious 

 matter. No process of nutrition can be con- 

 ceived to subsist in aniraals or vegetables, 

 without a separation of effete matters. We 

 know, indeed, that an organized body can- 

 not generate substances, but can only change 

 the mode of their combination, and that its 

 sustenance and reproduction depend upon 

 the chemical transformation of the matters 

 which are employed as its nutriment, and 

 which contain its own constituent elements. 



Whatever we regard as the cause of these 

 transformations, whether the Vital Principle, 

 Increase of Temperature, Light, Galvanism, 

 or any other influence, the act of transfor- 

 mation is a purely chemical process. Com- 

 bination and Decomposition can take place 

 only when the elements are disposed to 

 these changes. That which chemists name 

 affinity indicates only the degree in which 

 they possess this disposition. It will be 

 shown, when considering the processes of 

 fermentation and putrefaction, that every 

 disturbance of the mutual attraction sub- 



