CALAMITES AND LYCOPODS 373 



gametophytes may ultimately produce antheridia, and 

 the male ones, archegonia. It is of interest to note that 

 some of the fossil relatives of the modern horsetails were 

 heterosporus. 



The structure of the spores is unusual in that they bear 

 four ribbon-like appendages (elaters), formed from the 

 outer wall, and closely coiled around the spores (Fig. 267). 



FIG. 269. Equisetum palustre. Portion of a male prothallus, bearing 

 antherida; a, &, c, three antheridia in successive stages of development; 

 a. empty; sp, escaping sperms and sperm-mother-cells; c, antheridium 

 not yet opened; d, initial stage in the development of an antheridium. 

 X about 70. (After Sadebeck.) 



These appendages uncoil in dry air and recoil with moisture, 

 with a sharp, snapping motion, thus rolling the spores 

 about. 



The distribution of the spores is accomplished when 

 they are ripe, by the opening of the dry walls of the 

 sporangia. The shrinking of the walls gradually forces 

 out the spores, and by the uncoiling and snapping of the 

 elaters the spores become entangled and held fast to 

 each other in little flocculent masses. Thus the complete 



