94 EVOLUTION OF THE HIGHER PLANTS. 



heterosporous pteridophytes the gametophyte is dioe- 

 cious, and this is indicated by the two kinds of spores 

 large ones (macrospores) that produce female 

 plants, and small ones (microspores) that produce 

 males. 



Pteridophytes the highest plants in which the male 

 cells ( sperm atozoids) retain their primitive motile 

 condition, and recall the aquatic origin of the arche- 

 goniates. 



Sporophylls of the pteridophytes the first rudiments 

 of flowers. The "cone " of a lycopodium or equisetum 

 the hornologue of the flower of a pine. Both consist 

 of groups of special sporophylls. Microspore : pollen 

 grain ; macrospore : embryo sac. Pollen-sac and 

 ovule are morphologically sporangia. The seed is a 

 specially developed sporangium. 



In spermaphytes fertilization effected by the nucleus 

 of the pollen spore carried to the embryo-sac by the 

 pollen tube. 



Grymnosperms and angiosperms. Naked-seeded and 

 covered-seeded plants. 



Flowers of angiosperms usually have necessary 

 leaves (petals, sepals) specialized for protection and 

 attraction. The latter closely correlated with visits of 

 insects. 



Modifications of flowers and insects intimately asso- 

 ciated. Both mutually dependent to a great degree. 



Showy and edible fruits distributed by animals. 



Color, odor, nectar of flowers, lures to insects. 



Mechanical aids to cross-pollination. Dioecism ; 

 proterandry ; proterogyny. 



Special devices. Dead nettle ; sage ; orchids. Hum- 

 ming birds and flowers. 



