THE EVOLUTION OF SEX 



37 



and despite some exaggerations his general 

 conclusion survives that the progeny of 

 cross-fertilised plants are more successful and 



FIG. 7. Diagram of a flower. S, sepal; P, petal; ST, stamen 

 with anther (A) liberating pollen grains; P, pistil; 0V, 

 ovary enclosing an ovule which shows an embryo-sac 

 with the egg-cell (E), the endosperm nucleus (N), and 

 the antipodal cells (C); on the stigma are seen several 

 pollen-grains (PG) whose pollen-tubes are growing down 

 the style towards the egg-cell. (After Sachs.) 



more fertile than those of similar plants self 

 fertilised. Now cross-fertilisation will be more 

 readily secured if one of the germ-cells be 



