PERSPIRATION OF PLANTS. 9 



of many exotic succulent plants, as the different 

 species of aloe, &c. displays united pentagons or 

 hexagons. In the generality of plants the ducts 

 maintain no precise order in their direction, but are 

 curved in various ways, (lb. Fig. i, 2, 3.) 



They will remain not only when the cuticle is 

 gently detached, but will bear the friction of a 

 hair-pencil, even when the leaf has undergone 

 putrefaction. In my collection of skeletons of 

 leaves, I preserve the membranes of both surfaces ; 

 which, in order to cleanse them, I have handled 

 rather roughly without any injury to the vessels j 

 a strong proof of the firmness of their texture, 

 and their intimate connexion with the membrane 

 itself. 



It frequently happens, in separating the cuticle 

 from the fresh leaf, that some portion of the paren- 

 chymatous matter still adheres to the sides of the 

 ducts or to their interstices. Such particles appear 

 under the microscope like small orbicular bodies 

 or grains. (Fig. 1. & 4.) 



The lymphatic vessels are not only found on the 

 leaves, and leaf-like appendages of the stem and 



