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 J. 

 Itight, 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- 



