280 PHYLUM XIII. STROBILOPHYTA 



reality the distal portions of the ovules, and function as 

 photosynthetic structures for a year (or more). 



504. In the first summer or autumn an axial spore 

 mother-cell ("archespore") arises in the interior tissues 

 of the ovule, and this ultimately divides into four cells 

 (four young megaspores), only the lowermost of which 

 enlarges into the fully developed megaspore. By the 

 second spring this megaspore has divided and subdivided 



until a solid ellipsoidal cellular 

 mass is formed the gameto- 

 phyte. Then from certain cells 

 on the summit of the gameto- 

 phyte several (usually four) 

 sunken archegones arise, when 



FIG. 157. Pinus (archegonial, pvprvthincr i<5 rpflrlv fnr tViP pnm 

 andantheridialgametophytes). ( ^rytmng IS ready I( 



pletion of the process of fertili- 

 zation. In the meantime, the pollen tube resumes its 

 growth, bringing the two non-ciliated sperms to the 

 mouth of an archegone where one of the sperms soon 

 fuses with the egg, and fertilization is completed, a 

 little more than a year after pollination. 



505. By repeated subdivision and continued growth 

 of the zygote a cylindrical stem is formed, rooted below, 

 and with a whorl of narrow leaves above. This is the 

 sporophyte (or "embryo" of the seed). It is nourished 

 by the gametophyte tissue in which it is imbedded. In the 

 meantime ovule, "seed scale," and cone have increased 

 in size, and later the "seed scales" lose their chlorophyll 

 and become woody. Still later by the lessened supply 

 of water all parts of the cone become dry, stopping the 

 growth of the young sporophyte. The cone and seeds 

 are now "ripe," and by the spreading of the dry scales 

 the part of the seed containing the embryo is split loose 

 and blown away. 



