XIII 



EQUISETINEyE 



441 



in and joining the procambium zone of the cortex. At the point 

 of junction the cells are shorter and broader, and the cortical 

 cells lying outside are also much broader, so that the cortical 

 procambium is very conspicuous. If cross-sections are ex- 

 amined about this time, in the procambium zone are found a 

 number of groups of cells where the divisions are more rapid, 

 and the resulting cells narrower than the surrounding ones. 

 These are the separate vascular bundles, and are continuous 

 with those in the leaves (Fig. 230). The first permanent 

 tissue consists of one or two small annular tracheids upon the 



Fig. 230. — Longitudinal section of the young stem, showing the junction of the foliar and internodal 

 bundles ; ir, the primary tracheids ; x, x, tannin-bearing cells. 



inner side of the bundle (Fig. 229, C). These are followed by 

 several others. They first form in the internodal part of the 

 bundle and only later in the foliar portion. The nodal 

 tracheids joining the xylem of the foliar and internodal bundles 

 are very irregular short cells with annular thickenings upon 

 their w-alls. Later two small groups of larger spiral tracheae 

 are formed at the sides of the xylem, but the greater part 

 remains but little changed. By this time, in E. tehnateia, 

 numbers of cells with peculiar contents are noticed scattered 

 through the pith and cortex (Fig. 230). The contents of 



