30 THE LIFE-HISTORY OF A FERN 



medium of transit of the spermatozoids to the ovum. But the movements 

 of the spermatozoids are not subject to blind chance : the chemiotactic 

 attraction of the archegonium directs the spermatozoids through the water, 

 towards the open neck, which they may be seen to enter, and finally one 

 of the spermatozoids coalesces with the ovum : fertilisation is effected 





m 





V 



FIG. 14. 



Young embryo of Adiantum continuum. L = leaf-quadrant ; 5= stem-quadrant ; 

 R = root-quadrant ; /''foot-quadrant. (After Atkinson.) 



by the absorption of the male nucleus in that of the egg (Figs. 13 

 and i $ bis). Thus the presence of external fluid water is essential for the 

 process of fertilisation : without it the prothallus is unable to achieve that 

 object of its existence. 



The consequence of fertilisation is the growth and segmentation of 

 the ovum, or zygote, as it may now be called, to form a mass of 

 embryonic tissue, which at first remains embedded in the tissue of the 



