78 THE MECHANICAL FUNCTIONS. 



the surface of the cuticle, but more especially 

 in those that have a green colour.* They are 

 placed at nearly equal distances from one ano- 

 ther, 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 purpose of performing 

 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 conceives these orifices are 

 opened and closed. | 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 of the leaves, or on that of the stem. 

 This is the case with such aquatic plants as are 

 habitually immersed in water. In those that 

 are only partially immersed, stomata are met 



* Fig. 22 is a magnified representation of the appearance 

 in the cuticle of the Lycopodium denticulatum, taken in the 

 central part of the lower surface of the leaf, from De Candolle. 

 Fig. 21 is a still more magnified view of the stomata in the leaf 

 of the Lilium candidum, from Amici. 



f Ibid. IT. 215. 



