THE LIFE-HISTORY OF A FERN 



[CH. 



is gained through the open channel of the neck (Fig. 21, B). Thus the same 

 condition leads to the rupture both of the male and female organs. In nature 

 a shower of rain would supply the necessary water, which would serve also 

 as the medium of transit of the spermatozoids to the ovum. But the move- 



Fig. 21. Archegonia of Polypodium vulgare. A, still closed. 

 (7 = o\'um. j^'=: canal-cell. 7^" = ventral-canal-cell. B, an 

 archegonium ruptured. (X240.) (After Strasburger.) 



Fig. 22. Fertilisation in Onoclea sensibilis: the arrows indicate direction to the growing 

 point. ^ = a vertical section through an archegonium probably within ten minutes 

 after entrance of the first spermatozoid. ( x 500.) ^5 = vertical section of the venter 

 of an archegonium, containing spermatozoids, and the collapsed egg with a sperma- 

 tozoid within the nucleus. Thirty minutes. ( x 1200.) (After Shaw.) 



ments of the spermatozoids are not subject to blind chance. It has been 

 shown that diffusion into water of a very dilute soluble substance, such as 

 malic acid, serves as a guide, the spermatozoids moving towards the centre 

 of diffusion. Probably it is in this way that they are attracted to the neck 



