712 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



to the large amount of silica contained in the epidermal membranes. The earlj* 

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

 (e.g. E. arvense, fig. 403^), 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. — EquisetaceiB. 



1 Summer sterile Bhoot of Eguisetum arvense. 2 Vernal, spore-bearing shoot of Eguisetum arvense. s Fertile cone of 

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

 coiled. ? Equisetujn sytvaticuta witli cone. ^ Prothallium of a Horse-tail with antheridia. J, s, t natural size; ' x 3; 

 •x6; «, «X25; « x30. 



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. maximum, common in this country in damp places, attains a 

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



