CBYPTOGAMS 



205 



have true roots, — unlike Mosses and Liverworts, which 

 are attached only by hairs, or rhizoids. 



o4G. Under side of a segmeut of Fern 

 leaf, showing: sori. 



345. Rhizome and leaves of the 

 Rock Feru. 



347. Section of sorus : s, sporangia ; 

 /, indusiuni ; b, blade of the 

 leaf. — WossiDLo. 



479. Spores are borne in 

 small sporangia (Fig. 348), 

 clustered in groups on the 

 under sides of the leaves (Fig. 347). Each cluster, or 

 "fruit spot" (so)-us), is in many species shielded by a 

 membrane (iitdiisium, i). At maturity, and on the occa- 

 sion of certain conditions of moisture in 

 the atmospihere, the sporangium splits 

 at one side. Tlie top is slowly thrown 

 far back, and then suddenly resumes its 

 former place. The 

 spores are ejected by 

 the violence of the 

 motion. 

 480. The germination of the spore 

 results in the formation of a small, 

 thin, heart-shaped body called the 

 prothalliiim (Fig. 349), in shape and 

 habit of growth much resembling a 

 small thalloid Liverwort. Prothallia of common species 

 are from a quarter to a half inch in diameter, and may 



348. A sporangium. 



Fern prothallium : 

 ar, archegonia ; 

 an, antlieridia. 



