548 CONSERVATIVE ORGANS. [LECT. X. 



leaves in reference to their vascular, their cellular, 

 and their cuticular systems. 



a. Of the vascular system of leaves. 



Among fallen leaves which have been exposed 

 to the action of the atmosphere in a damp place, 

 or which have dropped into a pond, we generally 

 find some in which the cuticle and pulp are com- 

 pletely destroyed; whereas the ribs or veins, as 

 they are commonly but erroneously termed, being 

 less susceptible of decomposition, remain almost 

 entire, and display the appearance of a beautiful 

 tissue of network, more or less complicated. This 

 is the vascular system of the organ, and the leaf 

 in this state is termed a skeleton leaf. Leaves are 

 frequently artificially made into skeletons by ma- 

 cerating them in water until they begin to putrefy, 

 when the cuticle is easily separated by gently 

 rubbing and pressing them ; and the pulp washed 

 out from between the meshes of the vascular net- 

 work by rinsing in water : and if the operation 

 be carefully performed, the most minute cords of 

 vessels may be preserved * (see fig. 2, Plate 10). 



* Although skeleton leaves produced by spontaneous de- 

 composition must have been very early observed, yet they were 

 not artificially prepared until 164?5, when Marcus Aurelius 

 Severinus published a figure, with a description of a leaf of 

 Cactus Opuntia reduced to a skeleton. The art, however, was 

 little attended to, until it was revived by Ruysch, in the com- 

 mencement of the eighteenth century. This naturalist at first 

 prepared them, by covering the leaves with insects, which ate 

 away the pulpy part ; but as these anatomists, or satellites, to 



