DUCTS. 27 



this be examined with the naked eye, parts of brown 

 rings will be seen traversing the whiter portion of the 

 wood. These brown rings consist of woody fibre ; the 

 white portion of wood- cells. On making a very thin 

 transverse section, the interior of the woody fibres is 

 seen to be almost entirely filled up (PI. I. fig. 7 b), 

 while the cavity of the wood- cells is much more open 

 (PL I. fig. 7 a) the former also contain globules of 

 turpentine. 



It must be remarked here that some botanical 

 authors include both forms of woody tissue under the 

 term prosenchyma. But, as we shall see hereafter, 

 the form of the prosenchymatous cells being some- 

 times used as a character for distinguishing the cells 

 of leaves, to which the term pleurenchymatous cells 

 would be inapplicable, the above distinction will be 

 found important. 



Vessels } vascular tissue. In the next form of tubu- 

 lar cells, these are broader and softer than the cells of 

 woody tissue, thin-walled, and the ends pointed ; and 

 their walls exhibit spiral or ring-like markings, or 

 rows of dots (PI. I. fig. 5 c, e, b) , indicating the existence 

 of one or more spiral fibres or rings. When the vessels 

 contain spiral fibres, they are called spiral vessels 

 (PL I. fig. 5 c) ; when they contain ring-shaped por- 

 tions of fibre, they are called annular (an'nulus, a 

 ring) vessels (PL I. fig. 5 e) ; and when the spaces 

 between the fibres are partly filled up, leaving only 

 dots, the deposit forming a kind of network, we have 

 a reticulated (rete, a net) vessel (PL I. fig. 5 b). This 

 tissue can easily be obtained from a piece of cooked 

 rhubarb, the stem of a balsam, or from any soft- 

 stemmed plant. Vessels very frequently contain air. 



Ducts. The tubular cells forming ducts (PL I. 

 figs. 5 b, lie) are large, more or less flattened or blunt 

 at the ends (truncated) ; and the cell-membrane at 

 first closing the ends is often removed or absorbed, so 

 that the ducts communicate with each other, to allow 



