XII 



EQUISIITINEJE 



4^5 



prototype of the ''siphonostele," which he thinks is the condition 

 found in Equisctiuii. He seems, however, to have overlooked 

 the fact that in the adult shoot, at least, of Eqiiisetiim, the whole 

 vascular system of the stem orii^inates from the primary cortex 

 or perihlem, the original central tissue-cylinder giving rise only 

 to the pith. Moreover, his assumed ''ramular gaps" are found 

 equally developed whether branches are developed or not, and 

 are obviously related to the leaf-traces of the internode. 



All the cortical cells are separated by small intercellular 

 spaces, which are very conspicuous in the soft tissue of the 



Fig. 270. — Transverse section of the vascular bundle of a fully-developed vegetative 

 shoot, X75; i, i, lacunae; x, x, tannin cells; t, t, remains of the primary tracheids; 

 en, endodermis. 



fertile stems of E. tcUnateia and E. arvcnse. In all of the inter- 

 nodes of the main axes of E. tchnatcia chlorophyll is absent, 

 but in most species the principal assimilative tissue is situated 

 here. It consists usually of isolated masses of transversely ex- 

 tended green cells separated by strands of colourless sclerenchy- 

 matous fibres, which form the ridges so prominent upon the in- 

 ternodes and foliar sheaths. Seen in cross-section the masses of 

 30 



