l68 BOTANY. 



275. The prothallium. — In fig. 139 is shown one of these 

 growths enlarged. Upon the under side we see numerous 

 thread-like outgrowths, the rhizoids, which attach the plant to 

 the substratum, and which act as organs for the absorption of 

 nourishment. The sexual organs are borne on the under side 

 also. This heart-shaped, flattened, thin, green plant is the 



Fig. 139. 



Prothallium of fern, under side, showing rhizoids, antheridia scattered among and near 



them, and the archegonia near the sinus. 



prothallium of ferns, and we should now give it more careful 

 study, beginning with the germination of the spores. 



276. Spores. — We can easily obtain material for the study of 

 the spores of ferns. The spores vary in shape to some extent. 

 Many of them are shaped like a three-sided pyramid. One of 

 these is shown in fig. 140. The outer wall is roughened, and 

 on one end are three elevated ridges which radiate from a given 

 point. A spore of the Christmas fern is shown in fig. 141. 

 The outer wall here is more or less winged. 



