PTERIDOPHYTE8 



135 



face, more or less of the neck of the archegonium projecting 

 (Fig. 113). The eggs are not different from those formed 

 within the archegonia of Bryophytes, but the sperms are 

 very different. The Bryophyte sperm has a small body and 

 two long cilia, while the Pteridophyte sperm has a long 

 spirally coiled body, blunt behind and tapering to a point in 

 front, where numerous cilia are developed (Fig. 114). It 

 is, therefore, a large, spirally-coiled, multiciliate sperm, and 

 is quite characteristic of all Pteridophytes excepting the 

 Club-mosses. It is evident that a certain amount of water 

 is necessary for fertilization in fact, it is needed not only 



FIG. 117. Sections of portions of the gametophyte of Pteris, showing development 

 of archegonium: A, young stage, showing cells which develop the neck (a), and 

 the cell from which the egg cell and canal cells develop (6); B, an older stage, 

 showing neck cells (a), neck canal cell (&), and cell from which is derived the egg 

 cell, and the ventral canal cell (c); C, a still older stage, showing increased num- 

 ber of neck cells (a), two neck canal cells (6), the ventral canal cell (c), and the 

 cell in which the egg is organized (rf). CALDWELL. 



by the swimming sperm, but also to cause the opening of 

 the antheridium and of the archegonium neck. There 

 seems to be a relation between the necessity of water for 

 fertilization and a prostrate, easily moistened gametophyte. 

 Prothallia are either monoecious or dioecious (see 69). 

 When the prothallia are developing (Fig. 115) the anther- 



