324 



THE PTERIDOPHYTES 



314. Heterospory. Heterospory (meaning dissimilar spores) 

 arose in the pteridophytes with the establishment of two sizes 

 of spores, megaspores and microspores. Pteridophytes having 

 these are called heterosporous, and those with spores of the same 

 size, as in the common ferns (Filicales), are called homosporous 



(meaning similar spores). With 

 heterospory came also a differen- 

 tiation of the gametophytes into 

 male and female structures, the 

 first developing from the micro- 

 spores and the second developing 

 from the megaspores. 



315. The moonwort and 

 adder's-tongue. The moonwort 

 (Botrychium, Fig. 283, A) and the 

 adder's-tongue (Ophioglossum, 

 Fig. 283, B) are in the same 

 group (order Ophioglossales) and 

 illustrate certain primitive con- 

 ditions in the pteridophytes. 

 These forms do not have external 

 sporangia, as in the Filicales, but 

 the spores are developed in sunken 

 regions along peculiar stalks. 

 Such sunken sporangia are much 

 more primitive in structure than 

 those which develop upon the sur- 



A, the moonwort (Botrychium terna- <> i i PI 



turn) ; B, the adder's-tongue (Ophi- face of the plant,for they resemble 

 ogiossum vulgatum) more c i ose iy the conditions in the 



bryophytes where the spore mother cells are found in the interior 

 of the plant. The spore-bearing stalks are accompanied by sterile 

 blades devoted to the vegetative activities, so that these leaves 

 illustrate the same sort of division of labor as is found in the 

 royal fern (Osmunda regalis). The gametophytes are under- 

 ground, tuberous bodies generally, destitute of chlorophyll and 



FIG. 283. The moonwort and 

 adder's-tongue 



