ANGIOSPERMS 389 



climax in the evolution of the known plants and was fore- 

 shadowed in the massing of the sporophylls of the higher Pterido- 

 phytes. 



The most striking advances shown in the flower are as 

 follows : 



1. The evolution of floral envelopes for protection and for 

 attracting insects to aid in cross pollination. 



2. The change from radial symmetry to bilateral symmetry in 

 certain flowers. 



3. The progression from indefinite and numerous flower parts 

 to a definite and limited number. 



4. The change from free parts of hypogynous flowers to union 

 of parts as shown in perigynous, epigynous, epipetalous, sym- 

 petalous and synsepalous flowers, reaching the climax in the 

 composites. 



5. Dimorphism or flowers and flower parts shown in monaecism, 

 di'tcism, dichogamy, requiring cross fertilization. 



6. Proterandry and proten>gyny, also requiring cross fertiliza- 

 tion. 



Ninth. The development of the ovule case, or seed case, which 

 when young is a small and open carpel with exposed ovules, but 

 later infolds, thus enclosing the ovules which become seeds. 



Tenth. The seed, consisting of the ovule with its coats which 

 become the seed coats containing the embryo, and food sub- 

 stances. 



553. Formula for life history of the Angiosperms.* This 

 would be similar to that of the Gymnosperms and may be written 

 as follows: 



/Microspore Male Gametophyte sperm. 



(pollen grain) (pollen tube and contents) \ - 



Macrospore Female Gametophyte egg / 



(embryo sac) (embryo sac and contents) 



Fertilized egg Sporophyte, etc. In abbreviated form this be- 

 comes S / mi Sp ~ " S )FE S., etc. Starting with the 

 N ma sp FG e / 



* For reference only. 



