GYMNOSPERMS Q17 
the wind. In the pines and their allies the pollen grains 
are winged (Fig. 203, D), 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, ¢). Then the 
sperms are discharged, and when they reach the egg 
fusion takes place and fertilization is accomplished. 
126. Embryo.—The odspore 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 
