HORSETAILS. 



179 



Synapsis. 



The field 

 equisetum. 



Root. 



Shoot. 



Underground stem cr rhizome. 



Sterile shoot (branched, green, later than the fertile 



shoot). 

 Fertile shoot (early in the spring). 



Stem with nodes and internodes, crown of mem- 

 branous pointed leaves at the nodes. 

 Fruiting spike. 



Whorls of peltate spore-bearing leaves. 



Several sporangia on inner side of the 



sporophylls. 

 Sporangium contains 



Spores each with four elaters. 

 (The prothallium is not described here. ) 



Material and apparatus. — Entire plants including the underground root 

 stock may be preserved dry. The fertile shoots appear earlier, and should 

 be collected just as they are appearing from the ground ; the sterile shoots 

 should be collected later when they are well formed. 

 Apparatus, the same as in Chapter XXIV. 



