LECT. XI.] ANATOMY OF LKAVES. 599 



LECTURE XL 



OF THE CUTICULAR SYSTEM OF LEAVES! USE OF 



THE CUTICULAR APERTURES. OF THE APPEND- 

 AGES OF THE STEM AND LEAVES PUBESCENCE 



THORNS PRICKLES GLANDS PROPS: USES 



OF THESE APPENDAGES. 



EVERY leaf is covered with a real skin or epi- 

 dermis, which not only guards the vascular and 

 the cellular matter from external injury; but 

 is the medium by which it performs the important 

 functions of absorption and exhalation. In the 

 majority of leaves, the epidermis can be separated 

 from the parts it covers: and appears to be a 

 compound organ, or to consist of two distinct 

 layers; the exterior of which is a fine, transparent, 

 apparently unorganized pellicle, and the interior 

 vascular and cellular. But the opinions and de- 

 scriptions of phytologists are at variance on this 

 subject. Grew*, Malpighi "f~, Du Hamel J, Des- 

 fontaines, Mr. Keith ||, M. Kieser f , M. Mirbel **, 



* Anal, of Plants, p. 62. 



t Anat. Plantarum, p. 212. 



J Phys.des Arbres, i. 8. 



Mem. de Tlnst. Nat. i.4-81. 



|| Syst. of Phys. Bot. i. p. 313. 



5f Mem. sur F Organ, des Plantes t p. 141. 



** Elcm. de Phys. veg. i. 36.' 



