84 



STRUCTURAL BOTANY 



the leaves ; consequently every internode contains just as 

 many bundles as there are leaves at the node above, and 

 as the leaves alternate with each other at successive 

 nodes, so also do the bundles in the corresponding inter- 

 nodes. As all the bundles enter the stem to the same 



FIG. 39. Equisetum arvense ; transverse section of a branch of 

 sterile stem, x, xylem ;ph, phloem ; ca, carinal cavity ; en, 

 endodermis ; sc, sclerenchyma ; a, assimilating tissue ; vl, 

 vallecular cavities (imperfectly formed) ; st, stomata. 

 Magnified 45 diameters. (K. S.) 



depth, and then turn vertically downwards, it follows 

 that, as seen in transverse section, they always form a 

 single ring. It will be seen that the bundle-system is 

 just of the kind typical for Conifers and Dicotyledons, 

 but it is one of the very simplest examples of this type. 

 The stem is always ridged on the surface, as mentioned 



