Mosses, Ferns, and Horsetails. 



^93 



and stalk bearing it) and 

 more or less parasitic on 

 the sexual generation. 



180. Reproduction of 

 Ferns. — The sporangia 

 (Fig. 1 54) and the spores 

 contained in them are, in 

 some of the ferns, direct 

 descendants of a single 

 epidermal cell. In other 

 ferns they originate in 

 several cells of the epi- 

 dermis and deeper-lying 

 tissues. When the spores 



Fig. 156. 



C, archegonium of a fern with its 

 egg cell ; D, an antheridium with 

 sperm cells ; £, an empty anther- 

 idium ; ^ and G, motile sperms. 

 After Strasburger. 



Fig. 155. 



F, prothallium orgametophyfe of a fern seen on 

 its under surface. The hairs are the rhizoids. 

 At a are archegonia, at d antheridia. G, a 

 prothallium bearing a young fern plant or 

 sporophyte. After STRASBURGER. 



are ripe, the sporangia break open 

 elastically on imbibing moisture 

 and throw the spores to some 

 distance. When the spores ger- 

 minate, they do not immediately 

 produce the fern plant, but in- 

 stead, a small thin body known 

 as the prothallium (Fig. 155), 

 which lies flat on the substratum. 

 The prothallium, which may be 

 a centimeter or less in diameter, 

 bears on its under surface eggs 

 in archegonia, and sperms in 

 antheridia (see Fig. 156). 



The sperms are minute ciliated 

 bodies. They become discharged 

 from the antheridia and swim in 

 the rain water or dew in quest of 

 the egg, being attracted by a 



