448 



MOSSES AND FERNS 



CHAP. 



a nearer connection of these two groups than is usually admitted. 

 As in the eusporangiate Ferns, the antheridium mother cell is 

 divided into an inner and an outer cell of which the inner one 

 forms at once the sperm cells. When the antheridium arises at 

 the end of a filament, the divisions in the terminal cell are very 

 much like those in Osmund a. In the mother cell three intersect- 

 ing walls enclose a tetrahedral cell, which then has the cover cell 

 cut off by a periclinal wall. In both forms of antheridium the 

 subsequent history is the same. The central cell divides first 

 by a transverse wall, followed by vertical walls in each cell, and 

 subsequently by numerous divisions which show no definite 

 arrangement (Fig. 260, C), and produce a very large number 

 of sperm cells. In the cover cell only radial walls are formed, 



Fig. 261. — Development of the spermatozoids, Xiooo. A, Three of the central cells of 

 an antheridium before the final division; B-D, final nuclear divisions in the sperm 

 cells; E-J, development of the spermatozoid from the nucleus of the sperm cell; 

 K, two free spermatozoids; v, the vesicle; b, blepharoplast. (I. J., after Belajeff). 



and it thus remains single-layered, as in Marattia and Osmunda. 

 There is often a triangular cell (Fig. 260, D, 0), recalling the 

 opercular cell in these forms. 



From the prothallial tissue adjacent to the sperm-cells, there 

 is usually cut off a mantle of tabular cells enclosing the sperm- 

 cells, much as is the case in Marattia and Botrychium. The 

 dehiscence of the antheridium is caused by the separation of the 

 cells of the outer-wall, but no cells are thrown off. 



