70 



STRUCTURAL BOTANY 



The spermatozoids swimming through the water are 

 attracted by the archegonia. This remarkable fact, which 

 long remained an absolute mystery, is now so far ex- 

 plained that we have good evidence as to the nature of the 

 substance which attracts them. When a spermatozoid, 



as it makes its devi- 

 ous way through the 

 water, comes within a 

 short distance of the 

 neck of an open arche- 

 gonium, it turns aside 

 from its course, and 

 makes for the opening. 

 Here it finds the mu- 

 cilaginous drop, and 

 promptly plunges into 

 it. Its movements do 

 not cease, though in the 

 denser fluid they go on 

 more slowly ; the sper- 

 matozoid wriggles its 

 way down the neck, 

 through the mucilage 

 which fills it, and so at 

 last reaches the ovum 

 below. Quite a number 

 of spermatozoids may be 

 seen swarming around the opening of a ripe archegoniuui, 

 and several may penetrate down the canal, but probably 

 only one succeeds in uniting with the ovum. 



Now it has been shown by experiment that the 

 spermatozoids of Ferns are attracted by certain chemical 

 substances, and especially by malic acid. If artificial 



FIG. 36. Archegonium ready for fer- 

 tilisation, o, ovum ; n, neck ; m, 

 mucilage extruded from canal ; p, cells 

 of prothallus. Magnified 350. (After 

 Strasburger. ) 



