184 OF THE PARTS 



Mr. Knight has traced his central vessels, by which 

 the sap is conveyed from the root, into the flower and 

 fruit. On the returning sap in the bark of these parts 

 he has not been able to make any distinct observation ; 

 but he has determined that no matter of increase is 

 furnished from the flowers or their stalks, as from 

 leaves, to the part of the branch below them, nor in- 

 deed to any other part, Phil, Trans, for 1801,/?. S40. 

 There can be no doubt that certain parts of the flower, 

 which we shall presently describe, perform functions 

 respecting air and light analogous to those of leaves, 

 but entirely subservient to the benefit of the flower and 

 fruit. Their secretions, formed from the returning sap, 

 are confined to their own purposes. As soon as these 

 are accomplished, a decided separation of vessels takes 

 place, and the ripe fruit, accompanied perhaps by its 

 stalk, falls from the tree. Dr. Hales tried in vain to 

 give any flavour to fruit by the most penetrating and 

 volatile fluids conveyed through the sap-vessels; for 

 the laws of secretion are absolute in the organs of the 

 flower, and their various results are, if possible, more 

 strikingly distinct than even those we have contem- 

 plated in the leaves. 



It is scarcely necessary to repeat that the fructifica- 

 tion is essential to vegetables. A plant may be destitute 

 of stem, leaves, or even roots, because, if one of these 

 parts be wanting, the others may perfoim its functions, 

 but it can never be destitute of those organs by which 

 its species is propagated. Hence, though many indi- 



