2] 



THE VARIOUS GROUPS OF PLANTS 



55 



Pteridophyta 



Equisetineae : These are the Horsetails, of which the hving 

 examples are mere depauperated relics of a group which was much 

 more important in earlier geological ages, when it included larger 

 tree-like forms. Those remaining belong to a single genus of 

 perennial, herbaceous plants consisting of an underground stem 

 (rhizome) beset with fibrous roots, and sending up usually erect and 





Fig. 15. — Field Horsetail {Equisetum arvense agg.). A, sporophyte with fertile 

 branch (on right) and two young sterile branches ( X f ) ; B, mature sterile branch 



(x|). 



stiff, grooved aerial stems that are generally slender but hollow 

 and bear at the nodes (parts of the stem where leaves arise) close 

 whorls of rudimentary scale-leaves. The stem is commonly green 

 and photosynthetic, rarely more than a few feet high, and either 

 unbranched or, more often, bears whorls of slender branches (which 

 may themselves be much-branched) in the axils of the scale-leaves. 

 Fig. 15 shows a characteristic modern Horsetail. Such plants 



