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 paluslre. Portion of a male prothallus, bearing 
antherida; a, b, 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 
