LECT. III.J VASCULAR TEXTURE. 79 



of their calibers. They are composed of the 

 membranous texture, are firm, comparatively thick, 

 and somewhat pellucid. Linnaeus, following Ges- 

 ner, admitted the existence of three descriptions of 

 vessels only, which he named from their supposed 

 uses. The first he called vasa succosa, because they 

 carried fluids ; the second, utriculi, on account of 

 their being receptacles for preserving the vegetable 

 juices; and the third, trachece, or air-vessels*. 

 Willdenow-f also arranges them according to their 

 supposed uses, into, 1. air-vessels vasa pneuma- 

 tophora; 2. adducent vessels v. adducentla ; 3. 

 reducent vessels v. reducentia ; and, 4. lym- 

 phatics v. lymphatica: but every arrangement 

 founded on the supposed functions of the vessels 

 must be liable to objections. I think it preferable 

 to adopt the arrangement of Mirbel, with some 

 little variations, as it is constructed altogether on 

 the forms of the vessels. He describes six different 

 kinds of vessels J; but the whole may be arranged 

 under the three following genera : 



* "Constant vegetabilia triplicibus vasis: 1. Vasa succosa 

 " liquorem vehunt. 2. Utriculi alveolis succum conservant. 3. 

 " Trachea aerem attrahunt.'* Philos. Botan. 78. 



f Vide Principles of Botany, trans. 236. 



J " ], Les vaisseaux en chapelet ou moniliformes ; 2", les 

 41 vaisseaux poreux; 3, les vaisseaux fendus ou fausses trachees ; 

 "4, les trachees; 5, les vaisseaux mixtes ; 6, les vaisseaux 

 " propres." Elem. de Phi/s. veget. p. 31. 



