324 



PLANT STUDIES 



At the bottom of the conspicuous notch in the prothal- 

 lium is the growing point, representing the apex of the 

 plant. This notch is always a conspicuous feature. 



The antheridia and archegonia are usually developed on 

 the under surface of the prothallium (Fig. 293, A), and dif- 

 fer from those of all Bryophytes, except the Anthoceros 

 forms, in being sunk in the tissue of the prothallium and 

 opening on the surface, more or less of the neck of the 

 archegonium projecting (Fig. 294). The eggs are not dif- 

 ferent from those formed within the archegonia of Bryo- 



Fig. 295. Antheridium of Pteris (B), showing wall cells (a), opening for escape of 

 sperm mother cells (<•), escaped mother cells (c), sperms free from mother cells 

 (S), showing spiral and multiciliate character.— Caldwell. 



phytes, but the sperms are very different. The Bryophyte 

 sperm has a small body and two long cilia, while the Pteri- 

 dophyte sperm has a long spirally coiled body, blunt behind 

 and tapering to a point in front, where numerous cilia are 

 developed (Fig. 295). It is, therefore, a large, spirally coiled, 

 multiciliate sperm, and is quite characteristic of all Pterido- 

 phytes excepting the Club-mosses. 



When the prothallia are developing the antheridia begin 



