SEED-BEARING PLANTS 



397 



sporophyll, Fig. 295). In the Cycads and higher plants 

 the megasporangia are called ovules. 



355. Ovules. — The young megasporangia or ovules of 

 Cycads consist of two distinct regions of sterile tissue — an 

 inner nucellus, and an outer covering, or integument^ 



Fig. 293. — Megasporophyll (carpel) of Cycas media, bearing one ripe 

 naked (gymnospermous) seed, and three ovules which failed to become 

 seeds, doubtless through not being fertilized. (Compare Fig, 292.) 



which is an outgrowth of the ovule just below the nucellus. 

 The integument serves to protect the more delicate tissues 

 within, and later becomes transformed into the seed- 

 coat (Figs. 296-298). Only one of the four megaspores 

 develops within the nucellus. 



356. Female Gametophyte. — As in Selaginella, the mega- 

 spores begin to germinate while still in the sporangium, 

 but now a new feature is introduced into life history; 



