94 



STRUCTURAL BOTANY 



peculiar. They are apparently of endogenous origin, and 

 for a long time were thought really to arise below the 

 surface, though this is not the case. The branches are 

 arranged in whorls in the axil of each sheath, but alter- 

 nating with the leaf -teeth. The buds arise near the 

 growing-point, each from a single superficial cell, lying 



FIG. 43.- Equisctum arvcnse ; part of a radial section of stem, 

 just below the apex, to show exogenous origin of branch. 

 a, apical cell of branch ; 1 1} cortex of stem ; 1 2 , base, of leaf 

 below branch ; c, crevice between them, about to close up. 

 Magnified 360 diameters. (R. S.) 



immediately above the junction between leaf-sheath and 

 stem (see Fig. 43). 



This cell divides up so as to carve out a pyramidal 

 apical cell like that of the main stem, and the growth of 

 the branch now goes on in the usual way. But while it 

 still consists of a very few cells only, the leaf-sheath 

 grows out above it, and joins on to the tissue of the 



