118 



ANATOMY. 



may be incomplete, or spirally twisted (fig. 665), whence they have been mistaken 

 for old tracheae ; they, however, differ from tracheae in that they never present in their 

 earliest condition a regular and continuous spiral, and that many intermediate forms 

 between the ring and the spiral occur in every such vessel ; as, h-^vever, they termi- 

 nate in tapering cones, they have evidently the same origin as the tracheae. Reticulate 

 vessels are a modification of the annular ; if rings are so placed as to touch at 

 intervals, they resemble a network, and the same vessel may be both annular 

 and reticulate (fig. 666). Striate vessels are membranous tubes, cylindric or pris- 

 matic, the inner membrane of which resembles a web, whose interstices form thin 

 more or less regular striae. In prismatic vessels (fig. 667) the striae extend to 



the angles, and the 

 interstices resemble 

 the rungs of a ladder, 

 whence their name 

 of scalariform vessels. 

 Striate vessels ori- 

 ginate as a series of 

 superimposed cells ; 

 others as fibres, 

 as shown by their 

 spindle-shaped ends. 



604. Melon. 

 Annular 

 vessel. 



66.1. Melon. 



Spiral and 



annular vessel. 



fifiC. Melon. 

 Ilvtlciilute and 

 annular vessel. 



667. Brake. 



Rayed prismatic 



vessels. 



MR. Melon. D ited 



Punctate moniii- QQQ\ are membranous 



form vessel. ' 



tubes of which the 

 inner membrane is perforated by small holes forming parallel series of oblique or 

 horizontal dots; the vessel presents equidistant constrictions corresponding to 

 circular folds in the interior, clearly indicating 

 that the punctate vessel is formed by superim- 

 posed cells of which the connecting surfaces 

 have been absorbed. Punctate vessels with deep 

 constrictions resemble chaplets of beads, whence 

 their name of moniliform or beaded vessels. 



Laticiferous Vessels. We have seen that proper 

 vessels present inequalities resulting from the 

 modifications of the inner membrane ; there are 

 others with smooth transparent and homogeneous 

 walls, which contain a peculiar juice named the 

 latex (fig. 669) ; these anastomose, and form a 

 complicated network, of which the tubes meet at 

 right or acute angles; these tubes are usually 



fins, cheiidonium. cylindric, and swollen here and there (fier. 670), 



Laticiferous vessels. \ to /' 



670. Dandelion. 

 Laticiferous vessels. 



from the accumulation of latex in certain places ; 

 below these swellings the vessel is gradually constricted, and the communication 

 between the constricted and swollen portions is interrupted. The laticiferous vessels 



