THE SCOURING-RUSHES 



543 



4> rf^ 



Fig. 370. — Scouring-rush. ^4, male gametophyte or prothallus (i|fl) show- 

 ing antheridia (a, a). B-E, spermatozoids of various ages, much 

 more highly magnified. (Hofmeister, Schacht.) 



Fig. 371. — Scouring-rush. Female gametophyte or prothallus (*i^-) showing 

 archegonia (a, a, a) and pseudo-roots {h). (Hofmeister.) 



in a cone-like aggregation of whorled sac-leaves. Each of 

 these has a stalk ending in a shield-shaped expansion, six- 

 sided from pressure. Behind each angle of the shield is a 

 large sporangium dehiscing by a longitudinal slit (3, 4)- 

 The spores are peculiar in having four slender arms which 

 close tightly about the spore when moist, and spread apart 

 in drjnng, thus serving to eject the spores. They are there- 

 fore called elaters (5, 6, 7). 



The massive, much-lobed gametophyte bearing gametangia 

 above, and the comparatively large sessile sporangia of the scouring- 

 rushes, indicate a closer kinship with the adder-tongues than with 

 the true ferns, and suggest that the Equisetina^ may have evolved 

 from Hepatiese somewhat more moss-like perhaps than Anthoceros. 

 They may be characterized as plants similar to fertis except in having 



