THE ORIGIN OF SEX IN PLANTS 19 



together on the same plant (F. vesiculosus), in others the 

 male may be borne on one individual plant and the 

 female organs on another (Fucus serratus). Thus there 

 may be in Fucus not only a distinction of sexual cells but 

 also a sex-difference in the plants that bear them. 



FIG. 9. 



Cutleria, showing the smaller male, and larger female gametangia. Top-left are 

 small male gametes ; top-right are large female gametes. Below are three stages 

 of fertilization. (After Reinke.) 



The sexual cells of Fucus differ greatly in size. The 

 eggs are produced by division of the protoplasm of a 

 single large cell into eight parts. When ripe these are 

 set free into the sea-water as dense, non-motile spheres, 

 large enough to be seen with the naked eye (Fig. 10 (5) ). 

 Each is a naked mass of granular protoplasm, with a single 

 nucleus at the centre. The antheridial cells are smaller ; 

 and each produces, by cleavage of its protoplasm, sixty- 

 four minute spermatozoids (Fig. 10 (1-4) ). But notwith- 



