[ 5* ] 



circulation. That gentleman separated different por- 

 tions of bark from the rest of the bark in several trees, 

 and found that in most instances the separated bark 

 grew in the same manner as the bark in its natural 

 state. The experiment was tried with most success 

 on the lime tree, the maple and the lilac ; the layers of 

 bark were removed in August 1810, and in the spring 

 of the next year, in the case of the maple and the lilac, 

 small annual shoots where produced in the parts 

 where the bark was insulated.* 



The wood of trees is composed of an external or 

 living part, called alburnum or sap-wood, and of an in- 

 ternal and dead part, the heart-wood. The alburnum 

 is white, and full of moisture, and in young trees and 

 annual shoots it reaches even to the pith. The albur- 

 num is the great vascular system of the vegetable 

 through which the sap rises, and the vessels in it ex- 

 tend from the leaves to the minutest filaments in the 

 roots* 



There is in the alburnum a membranous sub- 

 stance composed of cells 9 which are constantly filled 

 with the sap of the plant, and there are in the vascu- 

 lar system several different kinds of tubes ; Mirbel has 

 distinguished four species, the simple tubes , the porous 

 tubes ) the trachea ', and the false trachea. ,f 



The tubes, which he has called simple tubes, 

 seem to contain the resinous or oily fluids peculiar to 

 different plants. 



* Fig. 3 represents the result of the experiment on the maple. Journal de 

 Physique, September 1811, page 210. 



t Fig. 4, 5, 6, and 7, represent Mirbel's idea of the simple tubes, the 

 tubes, the tracheae, and the false tracheae. 



