344 THE CONIFERS (GYMNOSPERMS) — FORESTS 
strobilus already described is made up of scales arranged 
spirally around a central axis. Each scale near its base 
bears two ovules. When the pollen is ripe, each grain, be¬ 
ing provided with wing-like air 
sacs, is easily blown about by 
the wind. Some of the pollen 
sifts into the carpellate cone 
through the .spaces between 
the scales, which at this time 
are separated slightly. Then 
the scales close up, the cones 
turn downward, and continue 
to grow for several months 
(Figures 317-321). 
Fruit. — During the next 
year, the pollen grains which 
are shut up inside the scales 
put forth pollen tubes and 
fertilize the egg Cells which 
develop in the ovules. From 
the fertilized eggs the embryo 
pines develop. 
When the cones are about two years old the scales open 
and allow the seeds to drop out. Each seed is provided with 
a wing by which it is blown about, _ 
for the pine depends on the wind to 
scatter its seeds as well as its pollen. 
Because the seeds lie on the scale 
without being inclosed in an ovary, all 
these plants are called gymnosperms 
(Greek, gymnos, naked ; sperma, seed). 
292. Habitat. — The evergreens 
grow in sandy soil in temperate or 
in cold climates, but a few of them occur where it is very 
warm. The finest evergreen forests in the world are found 
Figure 319. — Mature Female 
Strobilus or Cone. 
A , central axis; B, scales (sporo- 
phylls). 
Figure 320. - Pollen 
Grain of Pine. 
