322 



THE PTERIDOPHYTES 



spore fruits, or sporocarps, borne in groups on short stalks. 



These spore fruits (Fig. 281, A, s) are really modified portions of 



leaves, which are excellent illus- 

 trations of very highly developed 

 sporophylls, much more special- 

 ized than the spore leaves of such 

 ferns as Onoclea and Osmunda. 



The spore fruits burst open 

 when soaked in water through 

 the swelling of mucilage within, 

 and the contents come out as a 

 gelatinous, worm-like structure 

 bearing large groups (sori) of spores 

 along the sides (Fig. 281, B, so). 

 The spores are developed in es- 

 sentially the same manner as in 

 the common ferns (Filicales), but 

 the tissues of the sporangia are 

 so much modified that the re- 

 semblances, can only be followed 

 through a detailed developmental 

 study. The spores are set free 

 by the softening of the gelatinous 

 , , A material, and they begin to germi- 



A, male gametophyte withm micro- 



nate at once in the water. They 



gametophyte consisting of a single and are consequently called mega- 



m^gas^re^wh'fchTs fitted* Jtth spores and microspores. This con- 

 starch grains. D, a week-old em- dition is termed heterospory. 



bryo (slightly magnified) still at- ,, . ,, . 



tached to the megaspore: I, first ^ e megaspores are full of 



leaf; r, root. A, B, after Camp- starch grains, which furnish the 

 bell 



food for the development in a 



few hours of a small female gametophyte. This gametophyte 

 (Fig. 28.2, C) consists of a single archegonium at one end of the 

 spore. Although the cells are somewhat greenish, it is perfectly 



FIG. 282. Gametophytes of 

 Marsilia vestita 



spore: p, prothaiiial cells; two 



