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 mature pollen grain before the pollen is shed. A series 
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