4 6 



BOTANY OF THE LIVING PLANT 



are the sieve-plates which are perforated, while the cytoplasm that 



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. 



capita endod epid 



pith 



xylera 



phloem 





-H 



M 



^ 



Fig. 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, and points 

 towards the centre of the stem. ( x 150 ) 



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

 to have followed one of those 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 would be 

 met. They are elongated and pointed, with thick lignified walls 

 bearing 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 



