THE FIBRO- VASCULAR SYSTEM. 



115 



as described above, is in younger specimens composed 

 of parenchyma) is transformed into sclerenchyma (Fig. 



105). 



145 The fibro- vascular bundles of Ricinus communis 



have an arrangement in the stem, and a general structure 

 somewhat similar to those of Equisetum palustre, described 

 above. The limits of the bundles are so poorly marked that 



PP 



Fig. 104. Transverse section of the nbro-vascular bundle of the root of Acorw 

 calamus, s, bundle-sljeath (also called endodermis), with parenchyma outside and a 

 single layer of pericambiuni-cells inside ; pp. plates of radially-plac -d tracheary. 

 tissue ; ph, bundles of sieve tissue ; pp. narrow peripheral (and first formed) ves- 

 sels ; g, 14rge and still young vessel. After Sachs. 



in places it is impossible to tell whether the tissues belong 

 to them or to the surrounding ground tissues. 



The inner portion of the bundle (g, g, t, t, Fig. 106, and s 

 to t, Fig. 107) is made up of tracheary tissue of several varieties; 

 on the inner edge of this tracheary portion lie several spiral ves- 

 sels (s, s, Fig. 107) ; next to these, on their outer side, are sca- 

 lariform and pitted vessels (t, t, g, g, Fig. 106, I, t, t', Fig. 

 107), intermingled with elongated cells, whose walls are pitted 



