EQUISETALES (HORSETAILS) 435 



Some Plants Resembling True Ferns. — Some plants which 

 resemble the True Ferns, although they belong to another group, 

 are the Botrychiums or Moonworts that are common in the woods 

 {Fig. 388). They have an underground stem which sends up 

 leaves that have a finely divided vegetative portion and a spore- 

 bearing portion that much resembles clusters of small grapes. 



Fig. 389. — A section through the tuber-like gametophyte of Botrychium, 

 showing one archegonium and a number of antheridia in the upper surface. 

 X about 10. 



It is, however, in their gametophyte generation that they differ 

 most from True Ferns. Their gametophytes are tuberous sub- 

 terranean structures bearing the sex organs on the upper surface, 

 and associated with the gametophytes there is always an 

 endophytic Fungus {Fig. 389). 



Equisetales (Horsetails) 



The Equisetales, now represented by only one genus, Equisetum, 

 containing about 25 species, were numerous in ancient times and 

 some were tree-like in size. The Equisetums are best known by 

 their slender, grooved stems, called joint grass, common in fields, 

 around swamps, and along roadsides. The Field Horsetail 

 {Equisetum arvense) and the Thicket Horsetail {Equisetum Pratense), 

 both common in sandy fields and along roadsides and railways, 

 and the Marsh Horsetail {Equisetum palustre) and Swamp Horse- 

 tail {Equisetum fluviatile), common in swamps and around ponds, 

 are some familiar Horsetails. In fields they are often trouble- 

 some weeds. They range in height from a few inches to several 

 feet. The Equisetum robustum gets as high as 11 feet and a tropi- 

 cal species gets 40 feet high. The stems of Horsetails contain, 

 silica, and when dried and ground, they furnish a good scouring 

 powder. The Horsetails are called scouring rushes because the 

 stems of some are used in making scouring powders. 



