76 VASCULAR TEXTURE. [ LKCT - ni - 



different points; and, if the peculiar juices of the 

 plant be of a milky or coloured nature, as in 

 the Fig-tree or in any of the species of the genus 

 Euphorbia, they are still more clearly perceived 

 to issue from different points ; for instance, the 

 watery or colourless from one set, and the milky 

 or the coloured from another. This circumstance 

 leads us to conclude that the sap, or watery fluid 

 imbibed from the soil, is carried in one set of 

 vessels, and that the proper juices formed from the 

 sap by the vital powers of the plant, are conveyed 

 in another ; or, that there are conducting and re- 

 turning vessels : a fact which has been proved by 

 experiment, and which we shall afterwards fully 

 illustrate in speaking of the powers which move 

 the fluids in the vegetable body. 



The minuteness of these vessels requires the aid 

 of the microscope for their examination ; and even 

 by its assistance as they are not easily seen, owing 

 to their coats being in many eases transparent, and 

 the fluids contained in them colourless, we are 

 obliged, in order to render them more evident, 

 to have recourse to coloured fluids, which are 

 readily absorbed when the cut ends of twigs or 

 branches are immersed in them ; and the course 

 of the vessels through the branch is thus marked 

 by the colour. This mode of filling the vegetable 

 vessels has been termed injecting, the intention 

 of the process being the same as that which is 



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