CRYPTOGAMS 



251 



of these details as can be made out with help of the 

 magnifier. 



Some ferns have the sori covered with a shield (indusium), 

 others are naked, and still others are covered by a fold of 

 the frond. (Compare maidenhair and brake.) 



With a needle, lift an indusium and find the spore cases 

 (sporangia) underneath. Have they stalks? Draw a sorus 

 covered by the indusium, 

 also one having the in- 

 dusium removed. Draw 

 one sporangium. 



Spores. Lay a mature 

 fern frond upon a sheet 

 of white paper. Cover 

 it with another paper 

 until it is perfectly dry. 

 Then lift the frond and a 

 considerable quantity of 

 black or brown dust will 

 be found where the fern 

 frond has been lying. 



Suggestion The following ferns are very common. As 

 each has a peculiar manner of bearing its sporangia, it is 

 suggested that as many of them be studied as possible. 



Onoclea, the sensitive fern, shows marked differences 

 between the sterile and fertile fronds. It also has an inter- 

 mediate form which is interesting. 



Pteris, the brake, covers its sporangia with a fold of the 

 frond like a hem. 



Osmundas show three interesting modifications of fertile 

 fronds. In the cinnamon fern there is a beautiful brown 

 fertile frond. The royal fern has the fertile portion only 



I II 



FIG. 111. Prothallium of a common fern 

 (Aspidium). I, under surface, showing 

 rhizoids, rh, antheridia, an, and arche- 

 gonia, or ; II, under surface of an older 

 gametophyte, showing rhizoids, rh, and 

 young sporophyte, with root, w, and leaf ,6. 



