PTER1DOPHYTA. 



229 



having a bunch of cilia at each end ; the other species of Isoetes 

 have cilia only at the anterior end. 



The MACROSPORES. Shortly after 

 the macrospores have been set free, 

 or in Selaginella, while still en- 

 closed in the sporangium of the 

 mother- pi ant, they germinate and 

 soon become filled with the cellular 

 tissue of the prothallium, and even 

 in Selaginella the archegonium be- 

 gins to be formed before the rupture of the spore-cell-wall has 

 commenced (Fig. 235 A). 



The ARCHEGONIA are constructed on the same plan as those of the 



FIG. 234. Spermatozoidsof Selaginella: 

 b with a remnant of cytoplasm. 



FIG. 233. Macrospore of Selaginella : A longitudinal section, before the rupture of the 

 wall, six weeks after being sown. The endosperm (e) has not yet filled the entire 

 chamber. Cell-formation is still proceeding in the lower part of the spore. The endosperm 

 nnd prothallium (//)are separated by a distinct line (diaphragm). C G.;rminatiug macro- 

 spore seen from outside : s wall of the spore ; CB archegonia. 



FIG. 238. Archegonia of Selaginella : A unripe, in longitudinal section; c the central 

 cell; k neck-canal-cell, which is wedged in between the two-storied neck-cells; B ripe; 

 u ventral canal-cell ; C seen from above, open. It will be noticed that the neck is formed 

 of two tiers of four cells each. 



