18 



FORM AND ARRANGEMENT OF VESSELS. 



plants, in which the sap circulates rapidly. They consist of cylinders 

 more or less elongated, in which the thickening matter is so deposited 

 as to leave part of the membrane uncovered, thus giving rise to the 

 porous or pitted appearance. The uncovered portions of membrane are 

 sometimes absorbed in old vessels, and a direct com- 

 munication is established between them. The pores 

 have sometimes a bordered aspect, which, according 

 to Schleiden, depends on air contained in the cavities 

 between contiguous vessels. Porous vessels are usually 

 united to each other by a broad and often oblique 

 septum. 



37. This kind of vessel occa- 

 sionally presents a beaded appear- 

 ance, as if formed by porous cells, 

 with distinct constrictions at their 

 point of union (figs. 64, 65). This 

 articulated Bothrenchyma is by 

 some considered as a form of cel- 

 lular tissue (f 10, fig. 22). To 

 vessels exhibiting contractions of 

 this kind, whether spiral or porous, 

 the terms moniliform (monile, a 

 necklace), or vermiform (vermis, a 

 worm), have been applied; and the tissue composed of spiral, annular, 

 or porous moniliform vessels, has been denominated phleboidal (<pxtif , 

 <pA/3oV, a vein). 



38. Kiaticiferons vessels form the tissue called Cinenchyma (nivta, I 

 move, from certain movements of their contents, to be afterwards 

 noticed). They are the Milk-vessels, and the Proper vessels of old 

 authors ; and of late years they have been particularly examined and 

 described by Schultz. They consist of long, branched, homogeneous 

 tubes, which unite or anastomose freely (fig. 66), thus resembling the 

 vessels of animals. At first the tubes are very slender and uniformly 

 cylindrical (fig. 67 a), but afterwards they enlarge and present irregular 

 distensions at different parts of their course (figs. 67 b, 68), so as to give 

 rise to an articulated appearance. Their walls vary in thickness, and 

 are not marked by any depressions or fibres. These vessels are met with 

 in the inner bark, and they contain a granular fluid called latex, which 

 is at first transparent, but often becomes of a white, yellow, or reddish 

 colour. Endlicher and Unger state that they are formed by cells 

 united in a linear series, their septa being obliterated; while Meyen 



Fig. 63. Porous vessel (Bothrenchyma) from the Vine, showing its connection with woody 

 fibres, and the broad septa or partitions of the vessel itself. 

 Fig. 64. Porous vessel from Traveller's joy (Clematis vitalba). 

 Fig. 65. Moniliform porous vessels from the Common Balsam. 



