238 BOTANY. 



446. The macrospores are likewise produced within out- 

 growths (macrosporangia or ovules) upon certain modified 

 leaves. Only a few are produced in each outgrowth, and 

 of these rarely more than one become fully developed. 

 Moreover, the macrospores (here commonly called embryo- 

 sacs) never become free, but always remain within the 

 macrosporangium. 



447. We have seen that in the higher Fernworts the 

 parts of the plant-body bearing the spores are consider- 

 ably modified, often forming cones. In the flowering 

 plants this modification is carried still further, giving us 

 in the lower orders such structures as the cones of pines, 

 etc., and in the higher orders the many varied and beauti- 

 ful forms oiflotvers. 



448. The macrospore produces a sexual plant (gameto- 

 phore or prothallium) and one or more archegones, as in 

 the higher Lycopods. The archegones are usually much 

 simplified, and in the higher plants they consist of little 

 more than the germ-cells. The prothallium for the most 

 part does not develop until after the germ-cell has reached 

 maturity. It is a belated growth ; having lost nearly all of 

 its former usefulness as a supporting and nourishing tissue 

 for the sexual organs, its development is more or less re- 

 tarded. 



449. Fertilization of the germ-cell takes place essentially 

 as in plants of a lower grade. When the pollen-cell germi- 

 nates, it forms in a few cases a several-celled sexual plant 

 (prothallium), reminding us again of the higher Lycopods. 

 More commonly even this feeble growth of a prothallium 

 can hardly be detected. In either case the pollen-cell de- 

 velops a tubular filament, sometimes of great length. If, 



