100 



GYMNOSPERMS 



Each of these organs produces spores which upon germina- 

 tion develop, the former into female, the latter into male 

 gametophytes. 



(a) Carpellate Cones. The carpellate cones occur on short 

 lateral branches growing near the tip of the young apical 

 branches. Each cone has a central axis which develops 

 numerous thick fleshy outer protective scales and inner 

 macrosporangia or ovule-bearing scales. 



FIG. 57. White pine. The upper left figure is a staminate strobilus. 

 The upper right is a longitudinal section of the microsporophylls. The 

 lower left figure is the top view of the cross-section of the strobilus while 

 the figure at the right is the under view of the strobilus. 



A macrosporangium or ovule consists of an outer covering 

 or integument, a micropyle or circular opening in the integu- 

 ment which leads into the pollen chamber, the nucellus or 

 main body of the ovule and a megaspore or asexual spore. 



Development of the Female Gametophyte. The megaspore 

 upon germination divides into four cells. The three upper 

 cells dissolve and furnish nourishment for the lower reproduc- 

 tive cells. This cell by repeated division develops into the 



