PTERIDOPHYTA 



519 



around the spore. By means of their hygroscopic movements they serve to hook 



FIG. 486. Equisetum arvense. A, Fertile shoots, springing from the rhizome, which also bears tubers ; 

 the vegetative shoots have not yet unfolded. F, Sterile vegetative shoot. B, C, Sporophylls 

 bearing sporangia, which in C have opened. D, Spore showing the two spiral bands (elaters) 

 of the perispore. E, Dry spores showing the expanded spiral bands. (A, F, J nat. size. 

 B, C, D, E, enlarged.) 



together the spores, and in this way assure the close proximity of the unisexual 

 prothallia which the latter produce (Fig. 486 E). 



