190 



BOTANY AND PHARMACOGNOSY. 



assimilable materials, comprise the leptome and conducting- paren- 

 chyma (Fig-. 104). Water conducting elements, tracheal ele- 

 ments, comprise the vessels (trachese) and the tracheids, which 

 resemble each other except that the latter are single cells of 

 prosenchymatic shape, while the former are very long tubes, 

 varying from cylindrical to prismatic in shape and are arranged 

 in long rows in which they are superimposed lengthwise. 



The tracheae or vessels are formed by the disintegration and 

 removal of the transverse walls between certain superimposed 

 cells, forming an elongated cell or tube, which occasionally retains 

 some of the transverse walls (Fig. 102, A, B). The longitudinal 



Fig. 105. I, cross-section of a bast fiber of Begonia as seen by the micropolariscopc. 

 2, polariscopic view of a sphero-crystal of inulin in Helianthus tuberosus. After Dippel. 



walls are relatively thin and consist of lignocellulose, giving more 

 or less pronounced reactions with phloroglucin or aniline sulphate. 



Four types of vessels or tracheae are known : annular, spiral, 

 reticulate and porous. Those having tne thickenings in the form 

 of horizontal or oblique rings are known as annular trachea; 

 those having the thickenings in the form of spirals, which usually 

 run from right to left, are known as spiral trache.^ ; those 

 having the thickenings in the form of a reticulation are known as 

 reticulated trachea (Figs. 102, 175a, 191), and those with 

 spherical or oblique slit pores known as porous trachea or 

 vessels (Figs. 104, 220, 287, 303). 



In those vessels in which but few of the transverse walls are 

 obliterated, the walls are marked by both simple and bordered 

 pores, which latter are described under tracheids. Vessels contain 

 water, water-vapor and air; in some cases they contain sugar, 

 tannin, nnicilage or resin. 



