2C6 



STRUCTURAL BOTANY 



the pollen-sacs on the stamens is very constantly 

 four, in the Gymnosperms their number is subject to 

 very great variations. The dehiscence of each ripe 

 pollen-sac takes place separately by a longitudinal 

 slit 



Fig. 110. A, Male flower of Pinv.s pumilio in median lon- 

 gitudinal section. Magnified about 7 times. B, Longi- 

 tudinal section through a single stamen, showing one of the 

 pollen -sacs (p) below : s, apex of lamina. Magnified 14. C, 

 Transverse section of a stamen : p, p, the t\vo pollen-sacs. 

 Magnified about 20 times. D, A ripe pollen-grain : g, 

 small generative cell ; v, large vegetative cell ; w, wings 

 formed by inflated cuticle. Magnified 290 times. (After 

 Strasburger. ) For details of pollen-grain, see Fig. 111. 



Each pollen-sac arises from a small group of cells 

 on the under side of the stamen while it is still very 

 young. One cell of this group, lying immediately 

 below the epidermis, becomes the archesporium, and 



