LIFE HISTORY OF A GYMNOSPERM 



49 



or in small groups, "lateral along the new growth. Each terminates 

 a lateral axillary branch. A carpellate cone is composed of a main 

 axis which bears spirals of scales, by some termed megasporophylls 

 (carpels). Each scale is composed of an ovuliferous scale bearing 

 two ovules or megasori and a bract. Each megasorus contains a 



FIG. 23. Mature carpellate cones of white pine showing separated scales. 



nucellus or megasporangium which is surrounded by an integument, 

 except at the apex where an opening, the micropyle is evident. The 

 micropyle is the gateway to the pollen chamber which lies below it. 

 Within the nucellus occurs a megaspore or embryo sac. 



DESCRIPTION OF THE GAMETOPHYTE GENERATION 



The Gametophyte generation of the White Pine begins with the 

 development of the male and female gametophytes and terminates 

 with the fertilization of the egg. 



The Male Gametophyte. The male gametophyte commences to 

 form in the ^nature pollen grain before the pollen is shed. A series 



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