72 THE EVOLUTION OF PLANTS 



Fig. 7. (A) Pollen-tube of Microcycas, containing numerous 

 male cells X 90; (B) end of pollen-tube of Zamia, containing 

 the two ciliated spermatozoids; (C) a free spermatozoid, 

 showing the spiral band bearing the cilia (B and C X 80); 

 (D) longitudinal section of ovule of Cycas, showing embryo- 

 sac, nucellus with pollen-chamber, and integument slightly 



A after Caldwell; B and C after Webber; D after Griffith, 



