VEGETABLE ORGANIZATION. 77 



vegetables, certain organs, denominated Glands, 

 which are composed of closely compacted cells, 

 and which perform the function of secretion, 

 that is, the conversion of the nutritious juices 

 into particular products required for various 

 purposes in the economy of the plant. 



The external parts of a living plant require 

 protection against the injurious effects of the 

 atmosphere, and of the moisture it deposits. 

 For this purpose there is provided a membrane, 

 termed the Cuticle, which is spread over the 

 whole surface, investing the leaves and flowers, 

 as well as the stem and branches, and interposing 

 a barrier to the action of fluids, or other extra- 

 neous bodies, on the living organs. The cuticle 

 is formed originally by the condensation of a 

 layer of cellular tissue, of which the cells, being 

 consolidated by exposure to the air, and by 

 compression, compose a thin but impervious 

 pellicle. Amici has distinctly shown, by means 

 of his powerful microscope, the cellular structure 

 of the cuticle, and also that the layer of cells 

 of which it consists is independent of the sub- 

 jacent cellular tissue.* Fig. 20 is intended to 

 show this circumstance, the shaded part repre- 

 senting the cuticle with its series of cells. 



Oval orifices, or stomata, as they have been 

 termed, are discoverable on almost every part of 



* Annales des Sciences Naturelles, II. 211. 



