CHAPTER XIII 



EQUISETINE^ 



All of the living representatives of the second class of the 

 Pteridophytes may without hesitation be referred to the single 

 genus Equisetuin, with about twenty-five species, some of which, 

 e.g. E. ai'vense, are almost cosmopolitan. In the largest species, 

 E. giganteum, the stems reach a height of i o metres or more, 

 but are slender, not more than 2 to 3 cm. in diameter, 

 and supported by the surrounding trees and bushes. The 

 smallest species is E. scirpoides (Fig. 242, B), whose slender 

 stems are seldom more than i 5 to 20 cm. in length, and often 

 one millimetre or less in diameter. In spite of these differences 

 in size, the structure is remarkably uniform, both in gameto- 

 phyte and sporophyte. The following account is based mainly 

 upon a study of E. telinateia} but applies to the other species 

 that have been studied. 



TJie Prothalliuin 



The ripe spore of Equisetuvi is globular and shows no 

 trace of the ventral ridges usually evident in tetrahedral spores. 

 Four distinct membranes surround it, the inner one (intine) 

 being exceedingly delicate, but with care showing the cellulose 

 reaction.^ Outside of this are the exospore and the elaters, 

 between which lies another layer, " Mittelhaut " of Strasburger,^ 

 belonging to the exospore. The well-known elaters (Fig. 218, 

 A) form two strips attached in the middle and terminating in 

 spoon-shaped appendages. The elaters are usually more or 

 less spirally twisted, and when dry show faint oblique striations, 



^ E. maximum. - Buchtien (i). 



^ Strasburger, " Bau und Wachsthum der Zellhaute," p. 199. 



