PLANT WORLD CONTINUED 



241 



root. It is still imbedded in the gametophyte tissue from which it draws 

 its nourishment. 



The ovule, seed-scale, and cone, have increased in size in the mean- 

 time, the seed-scales losing their chlorophyl and becoming woody. As 



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 n ; 

 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 ; p, 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). 



