THE FIBBO- 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 



Fig. 104.— Transverse section of the flbro-vascnlar bundle of tlie root of Acorus 

 calamus. 8, bundle-sheath (also called endodermie), with parenchyma outside and a 

 single layer of pei-icambium-cells inside : ]7p. plates of radially-plac d (racheary 

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

 sels ; g, large and still young vessel.— After Kachs. 



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 {cf, 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 tliese, on their outer side, are sca- 

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

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



