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 
(5), showing spiral and multiciliate character. CALD WELL. 
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 
