ELEMENTARY ORGANS. 7 



parenchyma, the vesicles of which are compressed, and in a 

 firm state of cohesion. 



43. The spaces seen upon the epidermis, when examined by 

 a microscope, represent these vesicles. 



44. It is, therefore, not a peculiar membrane, but a form of 

 cellular tissue. 



45. It is spread over all the parts of plants which are ex- 

 posed to air, except the stigma (397). 



46. It is not found upon parts habitually living under 

 water. 



47. It is itself protected by an extremely thin pellicle, 

 which is apparently inorganic and homogeneous, and which 

 covers every part, except the openings through the stomates 

 (49). This membrane is the cuticle. 



48. The epidermis is furnished with stomates. 



49. STOMATES are oval spaces lying between the sides of the 

 cells, opening into intercellular cavities in the subjacent tissue, 

 and appearing to be bordered by a limb when they are viewed 

 from above 22 23 25 . 



50. This appearance. of a limb is owing to the juxtaposition 

 of two or more elastic vesicles, closing up or opening the 

 aperture which they form, according to circumstances, as is 

 manifest when the stomate is divided perpendicularly to the 

 plane of the epidermis 21 24 26 . 



51. Stomates are found abundantly upon leaves, particularly ^ 

 on the lower surface of those organs; occasionally upon all 



