122 



MORPHOLOGY OF TISSUES. 



without (not in transverse section), or as if the arched surface of the apex were 

 removed and spread out flat. If the segments are followed according to the 

 order of their numbering, and the path thus described is indicated by a continuous 

 line, a spiral is obtained, which is in reality an ascending spiral line, because each 

 segment lies higher than the older ones, as is shown in Fig. toi, B, where, 

 however, only two rows of segments are to be seen from without. The formation 

 of tissue begins by each segment breaking up, soon after its production, into two 



Fig. ioi. — Apical regions of the stem of an Equisetum ; A longitudinal section of an underground very strong bud ot 

 E. Telntatgia, in September (XSSo) ; B view of the apex from above (both from nature) ; C, D, E the same of E. ar-vense (after 

 Cramer). Q diagrammatic ground-plan of the apical cell and of the youngest segment ; D external view of a slender stem-apex ; 

 E transverse section through this from / to /) ; 5 is in all cases the apical cell, /, //, ///, &c. the segments ; i, 2, 3, &c. the 

 division-walls in the segments in the order of their formation ; x, y, b, bs in A the first rudiments of leaves. 



equal plates, a division-wall springing up parallel to the principal walls, indicated 

 in B, C, and 7? by i, i. Since in each of these two half-segments which lie one on 

 another the further processes are almost exactly the same, it is necessary to keep 

 in view only one half. Each half of the segment becomes divided first of all by a 

 vertical curved wall, which meets internally a side-wall, externally the centre of the 

 outer wall of the segment. Since three segments compose one section of the stem, 

 and each half-segment breaks up in this manner into two cells, the section of 

 the stem now appears as if composed of six cells or sextants, whose walls are 

 placed nearly radially, forming a six-rayed star, as is shown in the transverse section 



