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A TEXT-BOOK OF BOTANY 



under surface of the prothallium in the region of the. central 

 axis. When the prothallia are very young, the antheridia 

 begin to appear; and if the prothallia are poorly nourished 

 and stunted only antheridia appear. In mature, well- 

 nourished prothallia, however, archegonia also appear. In 

 consequence of their late appearance, the group of archego- 

 nia is near the notch, that is, near the growing point, while 

 the group of antheridia is farther back, on the older part of 

 the prothallium (Fig. 186, A). 



The antheridia and the archegonia are not free and pro- 

 jecting organs, as among the Bryophytes, but they are 

 more or less sunken in the tissue of the prothallium and 

 open on its surface. In the case of the archegonium only 



FIG. 187. Archegonium of a fern containing an egg (e), the neck being curved back- 

 ward toward the antheridia. 



the neck projects, and this is usually bent backward to- 

 ward the antheridia (Fig. 187). The egg resembles those 

 of all other archegonium-bearing plants; but the sperms 

 are very different from those of Bryophytes, having large 



