GYMXOSPERMS 217 



the wind. In the pines and their allies the pollen grains 

 are winged (Fig. 203, Z>), so they are well organized for 

 wind distribution. This transfer of pollen from the stami- 

 nate cone to the carpellate cone is called pollination, and 

 the agent of transfer is the wind. So abundant is the pol- 

 len of conifers that it sometimes falls like a yellow shower, 

 and the occasionally reported "showers of sulphur" are 

 really showers of pollen from some forest of conifers. Some 

 pollen must reach the ovules, and to insure this it must fall 

 like rain. To aid in catching the falling pollen the scale- 

 like carpels of the cone spread apart; and the pollen grains 

 sliding down their sloping surfaces collect in a little drift 

 at the bottom of each carpel, where the ovules are found. 

 In this position each of the most favorably placed pollen 

 grains begins to put forth a tube (pollen tube). This tube, 

 containing the two sperms in its tip, grows through the 

 ovule, and reaches the archegonia (Fig. 205, t). Then the 

 sperms are discharged, and when they reach the egg 

 fusion takes place and fertilization is accomplished. 



126. Embryo. The oospore that has been formed within 

 the archegonium at once germinates and begins to form the 

 young plantiet (embryo), which of course is still within the 

 ovule. This embryo continues to grow, feeding upon the 

 female gametophyte that surrounds it. It is evident that 

 this embryo is the young sporophyte of the next generation. 



127. Seed. While the embryo is developing, some im- 

 portant changes are taking place in the ovule outside of 

 the female gametophyte. The most notable change is the 

 formation of a hard, bony covering, which hermetically 

 seals the structures within, so that further development is 

 checked. In this way the ovule (sporangium) has been 

 transformed into what is called a seed, the distinguishing 

 structure of seed-plants. 



If a pine seed is cut open, the embryo (young sporophyte) 

 may be seen embedded in the center (Fig. 206); around 



