BUD OF EQUISETUM. 



217 



exterior. This apical cell divides by means of segmental walls, 

 which are parallel to the existing side-walls of the pyramid, follow 

 one another in spiral sequence, and form segments arranged in 

 three vertical rows. These segments (S) are shown in profile in 

 our Figure 85. They 

 further divide up in 

 definite fashion, and so 

 gradually construct the 

 body of the plant. At 

 some distance from the 

 apical cell, a " bank " is 

 raised upon the grow- 

 ing apex, which grows 

 at its edge with wedge- 

 shaped initial cells. 

 Certain parts of this 

 edge, later on, get in 

 advance in their de- 

 velopment, and form 

 the free leaf - apices 

 (" teeth ") of what is, 

 lower down, a connate 

 whorl of leaves (" leaf- 

 sheath"). The farther 

 removed from the 

 apical cell, so much the 

 greater are the young 

 leaf-whorls ; simultane- 

 ously the differentia- 

 tion of the inner tissue 

 of the stem progresses, 

 especially the separa- 



FIG. 86. Median longitudinal section through 

 main vegetative shoot of Equisetum ai*vense ; 



tion into denser, small- 



grow- 



pex of the main axis ; g, initial for a bud ; g', g", 

 l"", stages in the development of such a bud ; /, 

 m, differentiation 



11 ^ -t-u m ^ J '"> the origin of a root on the bud 



celled, thin nodes, and of the primary pith . rs> s piral vesse is making their 



less dense elongated- appearance ; w, differentiation of the nodal diaphragms 



( x 26). 

 celled, long internodes 



(Fig. 86). First the larger-celled pith begins to separate out in 

 the middle of the stem. In the fifth internode, counted from 

 above (in the figure), the first annular tracheides become visible 

 in the procambiun strings, at the outer limits of the pith, and can 

 be traced from here into the next higher commencement of a 



