82 VASCULAR TEXTURE. [LECT. Ill, 



slice of the wood to be examined must be cut, and 

 placed in a drop of pure water under a powerful 

 microscope. It has not been accurately ascertained 

 what kind of fluids is contained in these vessels. 

 A modification of the perforated vessels, having 

 the appearance of a string of beads 

 (fig./,), is named by Mirbel vaisseaux 

 en chapelet, beaded vessels. It con- 

 sists, as it were, of united portions of a 

 porous tube, narrowed at the extre- 

 mities and divided from each other by 

 perforated diaphragms. This variety 

 of the perforated vessels is found fre- 

 quently in roots, and at the going off 

 of branches and the attachments of leaves, being, 

 says Mirbel, " intermediate between the large ves- 

 sels of the stem and those of the branches ; and it 

 is by their meq,ns," continues he, " that the sap 

 passes from the one set of vessels into the other*." 



b. Annular vessels are so named from the per- 

 forations being transverse and oblong, as if the 

 tube were formed of rings, of the same 

 diameter, placed one above another, and 

 attached at some part of their edges, but 

 not touching throughout the whole circum- 

 ference. (Fig. g.) These vessels are in fact 

 porous vessels, with oblong transverse pores, 

 resembling in every respect, except in shape, 



* Eltm. de Phys. vtgtt. 1** Partie, p. 31. 



(flUK 



