118 



ANATOMY. 



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

 for old tracheie ; they, however, differ from traeheEe 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, however, 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 strige. 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 



fe 



:3 

 F— j 



spindle-shaped ends. 

 Dotted vessels (fig. 

 668) are membranous 

 tabes 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 headed 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 

 cylindric, and swollen here and there (fig. 670), 

 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 



(iB9. Chelidonium. 

 Laticiferous vessels. 



670. Dandelion. 

 Laticiferous vessels. 



