LIFE HISTORY OF A GYMNOSPERM 



PIG. 25. White pine (Pinus Sttobus). At left, megasporangium with mega- 

 spore in the center; above, pollen grains in the micropyle and pollen chamber. At 

 right, pollen grains beginning to germinate; the cells of the integument have 

 X enlarged and closed the micropyl< . (Gager, after Margaret C. Ferguson.) 



j e.n 



FIG. 26. White pine (Pinus Strobus). Vertical section through the upper part 

 of an ovule, shortly before fertilization, s.n., sperm-nuclei; st. c., stalk-cell; t.n. 

 tube-nucleus; arch, archegonium; e.n., egg-nucleus. (Gager, after Margaret C. 

 Ferguson.) 



