242 



General Biology 



brought the two non-ciliated sperm to the mouth of an archegone. One 

 of the sperm fuses with the egg which completes fertilization. This 

 fertilization takes place in the pines more than a year after pollination. 



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Fig. 145. I. The Gametophytes of the Pine. 

 A, diagram of a section of a year-old ovule; embryo sac with mature arche- 

 gonia ar imbedded in the tissue of the endosperm (female gametophyte) ; pollen 

 tubes (male gametophytes) growing down through the tissue of the nucellus »; 

 p c, pollen chamber; m, micropyle; i, integument. B, germinating pollen grains, 

 showing young male gametophyte; t, tube nucleus; g, generative nucleus; p, pro- 

 thallial cell. C, tip of pollen tube applied to the egg; t, tube nucleus; s, the two 

 sperm nuclei. D, a mature archegonium sunken in the tissue of the endosperm, 

 showing the large egg surrounded by a jacket of cells rich in protoplasm: two neck 

 cells of the archegonium shown just above the egg. — B, C, (After Miss Ferguson). 



II. The Sperm and Ovule of a Cycad (Zamia). 

 A, lower surface of a stamen, with numerous pollen sacs in two groups. B, 

 the two large top-shaped motile sperms at the end of the pollen tube ready to be 

 discharged above the archegonia. C, a sperm viewed from the end, showing the 

 spiral band which bears the cilia. D, diagram of a section of an ovule after polli- 

 nation; m, micropyle; i, integument; £, pollen chamber; n, nucellus containing 

 developing pollen tubes; a, archegonia, with large eggs imbedded in the endosperm 

 (female gametophyte).— B, C, (After Webber). 



III. — Diagram of the life-cycle of a pine. (After Schaffner.) 

 I., II., (From Bergen & Davis "Principles of Botany," by permission of 

 Ginn & Co., Publishers). 



