SEED-BEARING PLANTS 



431 



OUTLINE OF LIFE HISTORY OF PINUS 



The pine tree 

 (Sporophyte) 



Reduction 



Megaspore 



Embryo-sac 

 (Female gametophyte) 



Archegonium 



Microspore 



Pollen-grain 

 (Male gametophyte) 



4- 



(Antheridial cell) 



Sperm 



Oosperm 



4-i 



Embryo (In a seed) 



(Zygote) 



Embryo-rests 



4.4, 



Germination of seed 



4,4, 



Mature sporophyte (The pine tree) 



385. Comparison with Lower Forms. It will be spe- 

 cially instructive, at this point, for the student to make a 

 careful comparison of the life history of Pinus with the 

 lower forms, such as Cycas, Selaginella, Lycopodium, Equi- 

 setum, and a true fern, noting especially the relative impor- 



