116 



THE BOOK OF CHOICE FERNS. 



frequently not more than two being produced on one prothallus, and then 

 only one of them appearing fertile — originates, like the antheridia, from a 

 cell of the epidermis, from which it grows out in a hemispherical form. 

 These female organs are larger and more compact structures than the 

 antheridia ; their constitution is also totally different, for they are built with 

 four tiers of cells and in a sort of columnal form. Their development is 

 effected in this wise : A cell-wall forms, and cuts it off from the cell of the 

 epidermis. It increases in size, and becomes further divided into three layers ; 

 and these are again sub-divided by cell-walls. The result is that a structure 

 is formed somewhat in the form of a column, or, better still, of a flask with 

 a long, narrow neck. The hollow of the flask, or large cavity at the base, is 



occupied by a large cell, the oosphere 

 (see Fig. 7), rich in protoplasm, termi- 

 nating, when mature, in a kind of style 

 open at the top, and communicating with 

 the cavity below by means of a central 

 canal. The cavity or sac at the base 

 further contains a globose uticle, whose 

 functions are considered analogous to the 

 embryonic sac in the ovules of flowering 

 plants ; it surrounds the oosphere, which 

 is regarded as the object to be fecundated, 

 or as the germ that, after impregnation, 

 will set up a growth which ultimately 

 assumes the form of the parent plant. 

 From very careful observations it is now beyond doubt that the 

 fecundation of the oosphere is effected as follows : The tube of the neck of 

 the archegonium is at first filled with a narrow cell, the canal-cell, the cell- 

 wall of which becomes mucilaginous, swells, and is expelled from the outer 

 opening of the tube, leaving a passage for the antherozoid down the tube, or 

 central canal, to the oosphere, when the latter is ripe to be acted on by it 

 (see Fig. 7). The antherozoids are caught in the mucilage while moving over 

 the prothallus ; they wriggle down the tube, reach the oosphere, and fertilise 

 it. The oosphere very soon begins to grow, and the final result is the 

 development of the oospore into the leafy plant or Fern. It may be 



Fig. 7. Longitudinal Section of Mature 

 Archegonium of Fern 



(much magnified). 



c, Opening of Canal down Neck ; e, e, Epidermis of 

 Prothallus ; 11, Neck-cells ; o, Oosphere, 



