308 ANATOMY OF LEAVES. 



minate. Placing minute portions of the cuticle of 

 different leaves under the microscope, we can readily 

 ascertain the superficial form of these pores. Among 

 the varieties of the annulated aperture, we sometimes 

 find the space between the pore, or the shield and the 

 inclosing ring, divided into distinct portions ; and occa- 

 sionally a double ring, with the intervening space, al- 

 so, divided into four or more equal parts : examples 

 of the first variety are found on the lower disk of the 

 leaves of Lilac, Aucuba japonica, Hoya carnosa ; and 

 on the upper side of the leaf of the French Sorrel 

 [Rumex acetosa). The upper disk of the leaves of 

 the Sweet-scented Violet (f^iola odorata) affords a 

 good example of the double ring. But a very re- 

 markable form of the cuticular pore is observable on 

 the back of the leaves of the Oleander. It appears, 

 on a superficial view, a simple oval aperture without 

 any shield, but guarded by hairs which cross it in dif- 

 ferent directions ; and is comparatively much larger 

 than any of the other kinds of pores. 



The size of these pores are so small in the Myrtle, 

 Rose, Leguminous and Pink families, that 200 of 

 them, at least, might lie upon a geometrical line. 



In number the foliar apertures vary, also, in different 

 plants. The more minute they are, the more nu- 

 merous. On the lower surface of the leaf of Garde- 

 nia latifolia, we find an aperture in almost every 

 mesh ; but in the Aloe tribe scarcely one pore for 20 

 meshes, and on the leaf of Oleander, one among 60. 

 With regard to position, these apertures are in some in- 

 stances arranged in lines from the base to the apex of the 

 leaf, and have the same direction throughout ; but in the 

 majority of leaves they have no regular arrangement, 

 and assume different directions. In herbaceous plants 

 we generally find them on both surfaces of the leaves ; 

 but in ligneous plants they are scarcely ever seen on 



