422 



THE VASCULAR PLANTS 



77. Horsetails (Equisetales). — Equisetum means horse- 

 tail. It is the name of the only surviving group of the 



Equisetales. In an- 

 cient times other 

 groups of Equisetales 

 flourished and were 

 very abundant. 

 Now the only evi- 

 dences left to us of 

 these once great 

 groups are fossils 

 found in coal and in 

 other kinds of rock. 

 The horsetails or 

 equisetums are also 

 called the scouring- 

 rushes. Probably 

 you have seen them. 

 They have slender, 

 round, green stems 

 which are jointed, 

 and they are often 

 much branched in 

 such a way as to 

 suggest a horse's 

 tail. The stems are 

 stiff and rather brit- 

 tle. They may be 

 easily pulled apart 

 at the joints. A 

 ring of small, brown, 

 scale-like leaves oc- 



FlG. 215. — One of the horsetails {Equisetum 

 arvense). A, a vegetative shoot; note the scale- 

 like leaves at the joints. B, the fertile shoots 

 which, in this species, appear in spring before 

 the vegetative shoots ; note the cone-like strobili 

 at the tops ; these are composed of sporophylls 

 which are closely fitted together. C, a single 

 sporophyll. See page 424. 



