1J8 PROCESS OF NUTRITION. CHAP. III. 



which the central vessels were detected as before ; 

 but the colouring matter was found to have pene- 

 trated into the fruit also, diverging round the core, 

 approaching again in the eye of the fruit, and ter- 

 minating at last in the stamens. It was by means 

 of a prolongation of the central vessels, which did 

 not however appear to be accompanied by the spiral 

 tubes beyond the fruit-stalk. 



Such then are the parts of the plant through 

 which the sap ascends, and the vessels by which it 

 is conveyed. Entering by the pores of the epi- 

 dermis, it is received into the longitudinal vessels 

 of the root by which it is conducted to the collar. 

 Thence it is conveyed by the longitudinal vessels 

 of the alburnum, the small tubes of Mirbel, and 

 common tubes of Knight, to the base of the leaf- 

 stalk and peduncle ; from which it is further trans- 

 mitted by the central vessels of Knight to the ex- 

 tremity of the leaves, flower, and fruit. It is to be 

 regretted, however, that Mr. Knight's description 

 of the central vessels is not altogether so explicit 

 as could be wished. In trying to illustrate the 

 subject by synonym, he says indeed, that his cen- 

 tral vessels are M. Mirbel's tubular tissue.* But 

 this unhappily tends to obscure rather than to elu- 

 cidate the subject. For M. Mirbel's tubular tissue 

 consists of not less than five or six different species, 

 large tubes, small tubes, simple tubes, porous tubes, 

 spiral tubes, and mixed tubes. But to which of 

 * Phil. Trans. 1807- 



