52 



COURSE OF THE SAP. 



PT. II. 



than its organs require for their own perfect develop- 

 ment, the 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.' 

 Again : — 



' The power of absorbing nutriment from the atmo- 

 sphere, 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 neces- 

 sarily attended with an increase of nutritive power, and 

 a consequent further development of new leaves and 

 branches.' 



Again : — 



' 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 nutriment, 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 sufier a 

 change in colour, and fall off.' 



The Author of nature, and the author of the ' Che- 

 mistry of Physiology,' form their trees on widely 



