43° STRUCTURE AND LIFE HISTORIES 



stored as endosperm around the embryo. The remains 

 of the nucellus persist as a thin membrane surrounding 

 the endosperm (as mentioned above), the integument of 

 the ovule develops into the seed-coat, and from the integu- 

 ment there also develops a long, thin, membranous wing. 

 383. Seed-dispersal. — From the above description we 

 learn that it takes about a year and a half to make a pine 

 seed. When the seeds are mature, the scales of the car- 



"•5:';si. 





Fig. 320. -White pine {Pinus Slrobus). Late prophase in the first 

 nuclear division of the fertilized egg. The nuclear membrane has disap- 

 peared, and the chromatin from both egg and sperm may still be dis- 

 tinguished. X about 236. (After Margaret C. Ferguson.) 



pellate cone, which have now become large and woody, 

 spread apart (Figs. 308 and 309, D), and thus permit the 

 loose seeds to fall out. By means of the membranous 

 wing, the seeds are easily dispersed by the wind. 

 . 384. Germination of the Seed. — The seeds usually do 

 not germinate until the spring after they are dispersed, 

 or two years after pollination. Under suitable condi- 

 tions of environment the hypocotyl elongates, forming an 

 arch, and drawing the cotyledons out of the ground, 

 while the tap-root develops from the opposite end. "By 

 the straightening of the arch the green cotyledons are 

 lifted into the air and light, the hypocotyl elongates, the 

 root-system begins to develop, and thus the seedling 

 sporophyte becomes established as an independent plant. 



