712 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



to the large amount of silica contained in the epidermal membranes. The early- 

 spring shoots of many species are unbranched and terminate in spore-bearing cones 

 (e.g. E. arvense, fig. 403 2), whilst later on other branching shoots arise which are 

 sterile (fig. 403^). In other cases the fertile shoots are also branched (fig. 403'). 



Fig. 403.— Equisetaceoe. 



> Summer sterile shoot of Eqitiseium arvense. ^ Vernal, spore-bearing shoot of Equisetum arveTise. s Fertile cone of 

 the same. * A single sporangiferous scale (sporangiophore) of the same. 6 and 6 Spores with "elaters" exjianded and 

 colled. 7 Equisetum sylvatictim with cone. ^ Prothallium of a Horse-tail with antheridia. i, 2, 7 natural size; s x 3; 

 •x6; 5, s X 25; 8 X 30. 



The branches arise from the main axis in whorls at the base of the leaf-sheaths, 

 and in most cases perforate the latter as they develop (fig. 403'). They repeat the 

 structure of the main axis, save that they are smaller and have fewer teeth to their 

 leaf-sheaths. E. viaximum, common in this country in damp places, attains a 

 height of two metres, and is the largest British representative of the group, but 



