GROWTH OF PLANTS. 31 



p e: c 3 - /. development, the superfluous nutriment is not returned to 

 Me soil, but is employed in the formation of new organs. The 

 eoncnued supply of carbonic acid by means of a soil rich in 

 humus must exert a very marked influence on the progressive 

 cevelopment of the plant, provided the other conditions necessary 

 to the assimilation of carbon are also present. 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 disappear 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 necessarily attended with an increase of nutri- 

 tive power, and a consequent further development of new leaves 

 and branches. Leaves, twigs, and branches, when completely 

 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 performance 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 nutritive matters from the atmo- 

 sphere, and, with the aid of light and moisture, to appropriate 

 their elements. 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 

 formation 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 development 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 



