518 



A TEXTBOOK OF BOTANY 



[Ch. 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- 



Cy^ads 364 ' _Sp0r0phyllS and SPerm CdIS in tweenmicropyleand 



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



revoluta; xf. Right, above, microsporophyll of w ith a liauid Se- 

 Cycas circinalis, with microsporangia (anthers) on ^ . 



under surface. Below, sperm cells of Cycas revo- cretedby the tissues. 



iTnd Ikeno") (Fr ° m Kemer ' Richard ' and Hirase 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 



