280 PHYLUM XIII. STROBILOPHYTA 
reality the distal portions of the ovules, and function as 
photosynthetic structures for a year (or more). 
504. In the first summer or autumn an axial spore 
mother-cell (‘‘archespore’’) arises in the interior tissues 
of the ovule, and this ultimately divides into four cells 
(four young megaspores), only the lowermost of which 
enlarges into the fully developed megaspore. By the 
second spring this megaspore has divided and subdivided 
until a solid ellipsoidal cellular 
mass is formed—the gameto- 
phyte. Then from certain cells 
on the summit of the gameto- 
phyte several (usually four) 
. sunken archegones arise, when 
erg a oridicl wan etenet” everything is ready for the com- 
pletion of the process of fertili- 
zation. In the meantime, the pollen tube resumes its 
growth, bringing the two non-ciliated sperms to the 
mouth of an archegone where one of the sperms soon 
fuses with the egg, and fertilization is completed, a 
little more than a year after pollination. 
505. By repeated subdivision and continued growth 
of the zygote a cylindrical stem is formed, rooted below, 
and with a whorl of narrow leaves above. This is the 
sporophyte (or ‘‘embryo” of the seed). It is nourished 
by the gametophyte tissue in which it is imbedded. In the 
meantime ovule, ‘‘seed scale,” and cone have increased 
in size, and later the “seed scales’’ lose their chlorophyll 
and become woody. Still later by the lessened supply 
of water all parts of the cone become dry, stopping the 
growth of the young sporophyte. The cone and seeds 
are now “ripe,” and by the spreading of the dry scales 
the part of the seed SOnaanS the embryo is split loose 
and blown away. 
