PTERIDOPHYTES. 



103 



spores will be discharged covering the paper as a fine, brown 

 powder. If these are sown on fine, rather closely packed 

 earth, and kept moist and covered with glass so as to prevent 

 evaporation, within a week or two a fine, green, moss-like 

 growth will make its appearance, and by the end of five or six 



FIG. 66. A, spore of the ostrich fern (Onocled), with the outer coat removed. 

 B, germinating spore, x 150. (7, young prothallium, x 50. r, root hair. sp. 

 spore membrane. D, E, older prothallia. a, apical cell, x 150. F, a female 

 prothallium, seen from below, x 12. ar. archegonia. G, H, young arche- 

 gonia, in optical section, x 150. o, central cell. 6, ventral canal cell, c, 

 upper canal cell. /, a ripe archegonium in the act of opening, x 150. o, egg 

 cell. J, a male prothallium, x 50. on. antheridia. K, L, young antheridia, 

 in optical section, x 300. M, ripe antheridium, x 300. sp. sperm cells. 2V, 0, 

 antheridia that have partially discharged their contents, x 300. P, sperma- 

 tozoids, killed with iodine, x 500. v, vesicle attached to the hinder end. 



weeks, if the weather is warm, little, flat, heart-shaped plants 

 of a dark-green color may be seen. These look like small 

 liverworts, and are the sexual plants (prothallia) of our ferns 

 (Fig. 66, F). Kemoving one of these carefully, we find on 

 the lower side numerous fine hairs like those on the lower 



