518 



A TEXTBOOK OF BOTANY 



[On. XIII 



40 feet in height, and its crown of pinnate leaves recalls 

 its relation to the tree ferns. The plants are dioecious. 

 On the female plant the terminal bud produces from time 



to time a zone of 

 hairy brown sporo- 

 phylls, on the mar- 

 gins whereof are 

 huge orange-colored 

 ovules (Fig. 364), 

 which grow to large 

 size even without 

 fertilization. The 

 male plants produce 

 great terminal cones, 

 over a foot long, of 

 closely set sporo- 

 phylls which bear 

 many anthers (mi- 

 crosporangia) on the 

 lower surface. In 

 this and allied forms, 

 the pollen is carried 

 by wind to the 

 ovules, where themi- 

 cropyle, and an open 

 pollen chamber be- 

 sperm cells in tweenmicropyleand 



Left, megasporophyll, with ovules, of Cycas nucelluS, are filled 

 revoluta; X*. Right, above, microsporophyll of - th linnirl c P 



Cycas circmahs, with microsporangia (anthers) on ' 



under surface. Below, sperm cells of Cycas reco- Cretedby the tlSSUCS. 



Richard ' *** 



The partial evapora- 

 tion of this liquid 



draws the pollen grain into the chamber, where it develops 

 the tubes and effects fertilization, at its leisure, so to 

 speak, since several months intervene between pollination 

 and the actual fertilization. In this chamber is developed 



