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XXXVII. Memoir on the Anatomy of Vegetables, Read before 

 the Pbvjical Clafs of the Inftitute by C. MlRBEL. 



[Concluded from p. 179.] 



GHAP.vir. 



Of the Pores. 



A HE pores are fmaJi apertures formed in the membranes; 

 they'favour evaporation, abforption, and the motion of the 

 fluids. There arc three kinds of them. 



ift, The infenfible pores. — Thefe are apertures which can- 

 not he perceived by the eye even when affiited by the moft 

 powerful microfcopes. Effects, however, do not permit us to 

 doubt of their exiftence. Every vegetable tiffue is full of them, 

 as is proved by infenfible tranfpiration. What (hows at the 

 fame time their extreme finenefs is the phaenomenon exhibited 

 by an apple, or any other pulpy fruit, when placed below the. 

 receiver of an air-pump : the highly dilated air efcapes only 

 by burfting the (kin. 



2d, The elongated pores. — Thefe have been obferved by fe- 

 veral naturalifts, and particularly Decandolle, who gave them 

 the name of cortical pores. I (hall endeavour to complete 

 his defcription, bv uniting under the fame point of view his 

 obfervations and thofe which I have fince made myfelf. For 

 a knowledge of the principal facts I am indebted to his re- 

 fearches; but, as he confidered this fubject rather in a phyfical 

 than an anatomical light, his labour does not fuperfede the 

 neceifity of publifhing mine. 



The elongated pores exift only in the epidermis of the her- 

 baceous parts expofed to the air and the light. If the exterior 

 membrane of the vegetable be fkilfully removed, and if you 

 then examine it with a mierofcope, you will fee the interior 

 fides of the epidermis {till adhering, and which form as it were 

 a hexagonal net- work ; but here and there inftead of a hexagon 

 you will obferve an ellipfe, and the part of the epidermis cir- 

 cumfcribed by that elliptical area is cleft in a longitudinal di- 

 rection : the aperture is fometimes free, and fometimes ob- 

 ftructed : the latter cafe, in my opinion, arifes from the lips 

 of the pore, longer than is neceffary to (hut the aperture, being 

 applied one to the other, and intercepting the light. The elon- 

 gated pores are found commonlv in the Items, the branches, 

 the leaves, the bracteae, and even the herbaceous pericarpia. In 

 herbaceous plants the two furfaces of the leaves are covered 

 with pores; in the fat plants thev are lei's numerous than in 

 the other vegetables. In trees and fhrubs the inferior furfaee 

 only is in general pierced with thefe pores, The (terns when 

 3 * they 



