STRUCTURE.] DUCTS THEIR INTERCOMMUNICATION. 77 



are particularly abundant. They are among the largest 

 kinds of vessels. 



3. The Reticulated (Plate II. fig. 12./). In these the spiral 

 fibre, instead of separating into a number of distinct 

 rings, is continuous in some places, and anastomoses in 

 others, so as to form a sort of netted appearance. 

 Vessels of this kind, like the last, are found in the 

 stem of some herbaceous plants; as, for example, the 

 Garden Balsam, in which they may be seen in a great 

 variety of states. 



Some anatomists have added to the varieties above enumer- 

 ated, what they call strangulated vessels (vaisseaux en chapelet 

 or Strangles, corpuscula vermiformia, vasa moniliformia) . These 

 are determined by Bischoff to be mere accidental forms, 

 caused by their irregular compression, when growing in knots 

 or parts that are subject to an interrupted kind of develop- 

 ment. They may be found figured in Mirbel's Elemens, 

 tab. x. fig. 15.; and in Kieser, fig. 56. and 57.; but the best 

 view of their origin and true nature is in Slack's plate, 

 fig. 33., in the Transactions of the Society of Arts, before 

 referred to. Link defines them to be short spiral vessels 

 with attenuated extremities, and regards them, in his latest 

 works, as young spiral vessels, or as the commencement of 

 spiral vessels, which, instead of lengthening, grow together 

 by their ends. 



Vascular tissue always consists of tubes that are unbranched. 

 They have, indeed, been represented by Mirbel as ramifying 

 in some cases : but this opinion has undoubtedly arisen from 

 imperfect observation. When forming a series of vessels, the 

 ends of the tubes overlie each other, as represented in Plate II. 

 fig. 15. 



There is no doubt that the membrane is obliterated at the 

 place where two vessels touch each other, so that a hole is 

 formed, or that transverse bars remain under the form of a 

 grating : the latter appearance is produced by the remains of 

 the spiral fibre, some of whose convolutions are partially 

 uncovered in consequence of the absorption of the enveloping 

 membrane. By this simple contrivance all the forms of 



