374 



GENERAL MORPHOLOGY OF PLANTS 



synthesis taking place in the green stem. The fruiting part of 

 the stem forms a spike or cone at the apex of certain stems. 



Most of the species of 

 equisetum grow in sandy 

 places, especially along 

 railroad or other embank- 

 ments, in soil where few 

 other plants grow. This 

 is interesting as it shows 

 how a group of plants 

 which was much more 

 abundant in the past 

 preserves itself from ex- 

 tinction by being adapted 

 to grow under conditions 

 where few other plants 

 can. Some of the equi- 

 setums, however, grow 

 in swamps where other 

 vegetation is dense. The 

 genus Equisetum is the 

 only genus in this class. 

 It is the only representa- 

 tive of a class of plants 

 which flourished in geo- 

 logical times during the 

 " Carboniferous Age." 



Fig. 339- 



Portion of Many of the representa- 



Fig. 338- 



Sterile plant of horsetail (Equi- 

 setum arvense). 



fertile plant A . , ., 



of Equise- tives then were tree-like 



turn arvense, - i < M 



showing forms, and fossil remains 



whorls of - , . , i i j 



leaves and are found in the coal beds 



the fruiting . 



spike. formed at that time. 



There are now about twenty-five living species. 



527. The fruiting spike or cone. This is well studied in 

 the common field horsetail (E. arvense) which is common in 

 damp sandy places in fields and along railroads. There is an 



