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 arven'se) 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 1 1 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. 



