452 PHARMACEUTICAL BOTANY 
After pollination the carpellate cone gradually bends on its 
axis so as to ultimately reverse its position and hang downward. 
FERTILIZATION.—About a year after pollination the pollen 
tubes, lying within the pollen chamber show signs of renewed 
activity. ‘The tube nucleus passes to the tip of the tube. The 
Pe generative-cell divides to form a 
body and a stalk-cell which pass 
into the tube. The body-cell 
later forms two sperm nuclei. 
While these changes are taking 
place the tube is penetrating the 
nucellus and growing toward the 
embryo sac with its contained 
female gametophyte. It finally 
enters it, passing between the 
neck-cells of the archegonium. 
The tip of the tube then breaks 
and the entire tube contents is 
emptied into the egg. One of 
the sperm nuclei fuses with the 
t | egg nucleus and fertilizes it form- 
| ing an odspore or zygote. The 
aii 4} odspore contains the diploid 
Fic. 340.—White pine (Pinus Strobus), NUMber of chromosomes. 
Vertical section through the upper part = SEED FORMATION AND Dis- 
peepee a Faia nha) a TRIBUTION.—The odspore under- - 
tube-nucleus; arch, archegonium; en, Z0€S repeated divisions and 
egg-nucleus. (Gager, after Margaret C. forms the embryo or young sporo- 
Ferguson.) phyte plant and a suspensor to 
which it is attached. The embryo is nourished by a portion of 
the prothallus but the greater part of the prothallus forms the 
endosperm tissue of the seed surrounding the embryo. The thin 
nucellus persists as an endosperm covering. The integument 
becomes modified to form the hard protective seed coat. A por- 
tion of the scale of the cone directly above and adjacent to the 
ovule forms a membranous wing which separates from the scale 
as part of the seed. 
