110 PHYSIOLOGY OF VEGETALES. 



The arteries in the limbs are deep-seated near the 

 bones, while the veins are much more superficial. 



III. Of the Sap-vessels, course of the Sap, functions of 

 the Leaves, and theory of Vegetation. 



The whole vegetable body is an assemblage of tubes 

 and vessels, as has been previously observed. 



Observation. In the arrangement of these there is a degree of 

 similarity in all plants, but each species has its peculiarities just 

 as it has in external characters. 



The fluid which is most abundant in these vessels is 

 the sap or blood of the plant, from which are secreted by 

 appropriate organs, all the various vegetable products 

 to which the various flavours and qualities of each plant 

 are owing, as gums, resins, honey, acids, essential oils, 

 &c. These substances must each be lodged improper 

 cells and vessels to be kept distinct from each other. Air 

 is found to exist in the vegetable body, and must like- 

 wise be contained in appropriate vessels. 



1. Of me, Sap-vessels and Cortical-vessels, and their 

 communication with each other in the leaf. 



The external surface of the radicles or fibres of the 

 roots, are presumed to be perforated by the mouths of 

 innumerable vessels which absorb nourishment. 



These absorbents are presently collected into the 

 large simple vessels of the sap-wood, which are com- 

 pared to the veins of an animal. The sap-vessels, 

 called by Mr. Knight central vessels, from their situa- 

 tion near the pith in young plants, pass up and branch 

 off to the leaves and fructification, as they approach 

 them. 



Passing through the woody part of the foot-stalks 

 of the leavef, and through the ribs and veins of the 

 leaf, which are its ramifications, they are presumed 

 to terminate in the -parenchyma or pulp of the leaf, and 

 communicate with the vessels and cells which compose 

 it. Thus they extend from the fibres of the root to the 



