ANATOMICAL STUUCTUIIE OF LEAVES. 95 



These are the glands ah'eady referred to. They are firm 

 fleshy bodies, resembling little convex buttons ; and 

 are composed of cells, arranged in a circular manner, 

 round an axis, consisting of two such cells, stationed 

 one on the top of the other {Jig. 4. & 5.). I presume 

 that these glands are analogous to the curious hairs of 

 Sun-dew, although we do not see that they are pos- 

 sessed of any irritability ; but in the Sun-dew they 

 arise from a general expansion of the cuticle, and 

 not from spurious stomates. 



The cuticle of the under-side of the leaf is similar 

 to that of the upper ; but it is destitute of glands 

 {fig. 1. e. ^ fig- 3.), in lieu of which little clusters of 

 transparent greenish hairs {f.) grow from the abortive 

 stomates. These hairs are each composed of one 

 single cell, and may be considered a rudimentary form 

 of the glands of the upper surface of the leaf {figs. 6. 

 & 7')* ^^ t^® under surface, however, you will find, 

 in addition, a considerable number of true stomates, 

 or breathing pores {fig. 3. a a a.). What those organs 

 are, and for what purpose they are believed to be 

 intended, has already been explained to you (\^ol. I. 

 p. 103.). 



Immediately beneath the cuticle of either surface 

 of the leaf lies the parenchyma, or pulpy part {fig. 

 1. c c), composed of several layers of cells, gradually 

 growing larger, more transparent, and thinner-sided, 

 as they approach the middle. The cells of paren- 

 ch)-ma are supposed to be the principal seat of diges- 

 tion and respiration. The food of the plant is pro- 

 pelled into the leaf through the woodv tubes. 



