CH. XII] THE HORSETAILS 501 



which the leaves are reduced merely to sheathing scales. 

 The cones of sporangia are always terminal. In some 



FIG. 354. Equisetum arvense. 



Left, a sterile, green, shoot ; next two fertile, uncolored, shoots ; X \> 

 .[tight, below, a strobilus, showing shield-shaped sporophylls, with sporangia, 

 X 2 ; above, one of the latter, X 6 ; uppermost, spores, with elaters coiled 

 and uncoiled, X 20. (From Kerner.) 



species the rush-like stems are green, columnar, and un- 

 branched, but in others the cone-bearing stem is without 

 chlorophyll, while a separate shoot is green and usually 

 branched in whorls in a way to suggest the name Horsetails 

 (Fig. 354). The tissues are rather remarkably differen- 



