THE TISSUES OF THE STEM 



39 



lines the tubes is collected in a mass above each plate. The tubes 

 are embedded in long prismatic cells of the phloem-parenchyma, 

 and in this stem no bast-fibres are present. 



The cambium consists of long, very narrow cells, with thin walls 

 and dense protoplasm. In each radial row of them the cells are as a 

 rule of the same length, showing that they are the result of division 

 of a single parent cell. 



epid 

 xylem 



pith 

 I 





camb 



f 



i r 



endod 

 phloem ; cortex 



-^ 



F G. 24. 



Median longitudinal section through a vascular strand of Scrophularia nodosa, 

 similar to that shown in Fig. 23. The arrow indicates the pore of a stoma. ( x 150.) 



The xylem is more varied in structure, and if the section happened 

 to have followed one of these radial series of vessels seen in the trans- 

 verse section, its appearance would be as shown in Fig. 24. Starting 

 inwards from the cambium, a series of fibrous tracheides v/ould be met. 

 They are elongated and pointed, with thick lignified walls bear- 

 ing small pits. They surround and embed a larger pitted vessel, 

 which appears as a wide tube without any protoplasmic contents, 

 and is limited by a thick, pitted, woody wall. About half-way down 

 the section it is marked by a ring ; this indicates where an oblique 

 septum divided two of those cells from the fusion of which the vessel 



