68 THE MECHANICAL FUNCTIONS. 



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 

 subjacent cellular tissue.* Fig. 20 is intended to 

 show this circumstance, the shaded part represent- 

 ing the cuticle with its series of cells. 



Oval orifices, or stotnata, as they have been 

 termed, are discoverable on almost every part of 

 the surface of the cuticle, but more especially in 

 those that have a green colour.-)" They are placed 

 at nearly equal distances from one another, and are 

 particularly numerous in the cuticle of the leaves, 

 where they occupy the intervals between the fibres. 

 These orifices conduct into the interior of the plant, 

 probably into the general cavity of the intercellular 

 spaces. It is evident, from the functions they 

 perform, that they must occasionally open and 

 close ; but the minuteness of their size precludes 

 any accurate observation as to the nature of the 

 apparatus provided for the performance of these 

 motions. Amici describes their margins as formed 

 by two cells, by the movements of which, combined 

 perhaps with those of the adjoining cells, he con- 

 ceives these orifices are opened and closed. J Great 

 variety, however, is observable in the structure of 

 the stomata in different species of plants. 



Many plants have no stomata, either on the cuticle 



* Annales des Sciences Naturelles, ii. 211. 



f Fig. 22 is a magnified representation of the appearance in the 

 cuticle of the Lycopodimn denticulatum, taken in the central part 

 of the lower surface of the leaf, from De Candolle. Fig 2 1 is a 

 still more magnified view of the stomata in the leaf of the Lilium 

 candidum, from Amici. 



X Annales des Sciences Naturelles, ii. 215. 



