VII.] THE BRACKEN FERN. 59 



tion, which developes a similar process, the primitive rootlet, 

 close to the spore. The hypha-like prolongation, at first, 

 undergoes transverse division, so that it becomes converted 

 into a series of cells. Then, the cells at its free end divide 

 longitudinally, as well as transversely, and thus give rise to 

 a flat expansion, which gradually assumes a bilobed form, and 

 becomes thickened, in some parts, by division of its cells in 

 a direction perpendicular to its surface. The protoplasm of 

 these cells developes chlorophyll granules, whereby the bilobed 

 disk acquires a green colour ; while numerous simple radicle 

 fibres are given off from its under surface, and attach the 

 little plant, which is termed a prothallus or prothallium, to 

 the surface on which it grows. 



The prothallus attains no higher development than this, 

 and does not directly grow into a fern such as that in which 

 the spores took their origin; but, after a time, rounded or 

 ovoidal elevations are developed, by the outgrowth and division 

 of the cells which form its under aspect. Some of these are 

 antheridia. The protoplasm of each of the cells contained in 

 their interior is converted into an antherozooid, somewhat 

 similar to that of Chara, but provided with many more cilia. 

 The antheridium bursts, and the antherozooids, set free from 

 their containing cells, are propelled through the moisture 

 on the under surface of the prothallus by their cilia. 



The processes of the second kind acquire a more cylin- 

 drical form, and are called archegonia. Of the cells which 

 are situated in the axis of the cylinder, all disappear but that 

 which lies at the bottom of its cavity. This is the embryo 

 cell, and when the archegonium is fully formed, a canal leads 

 from its summit to this cell. The antherozooids enter by 

 this canal, and impregnate the embryo cell. 



The embryo cell now begins to divide, and becomes 

 converted into four cells ; of these, the two which lie at the 

 deepest part of the cavity of the archegonium subdivide and 



