288. PHYLUM XIV. ANTHOPHYTA 
finally takes the form of a very small stem, tipped with 
a root at one end, and bearing two rudimentary leaves 
at the other. In the meantime the immature game- 
tophyte resumes its development as the result of the 
union of the second sperm nucleus with the two polar 
nuclei to form the so-called endosperm nucleus, which by 
its rapid division, with much delayed formation of cell 
walls, results in the development of a mass of tissue 
surrounding and nourishing the embryo sporophyte 
’ and filling the growing ovule. It is now known as the 
endosperm, but it is in reality only the belated game- 
tophyte. 
522.. The ovule has now grown much in size. Ex- 
ternally its outer coat has become thicker and harder, 
while internally the gametophyte has enlarged and solidi- 
fied. A layer of cells at the base of the ovule now 
becomes corky and checks the supply of water, drying 
and hardening the whole ovule, and stopping further 
growth. In this final state the ovule is called the 
seed. 
523. In the Buttercup the carpel enlarges to accom- 
modate the growing ovule, but finally its tissues harden 
and dry so that when the seed is mature it is contained 
within the close-fitting wall of the old carpel and, in this 
condition, it finally falls off from the flower axis and is 
known as a fruit. The term “fruit,” therefore, is here 
used for the ripened carpel and its contained seed, and 
in flowering plants this is the generally accepted signi- 
fication of the term. 
524. When these fruits fall to the ground and absorb 
moisture, the embryo plant in each seed renews its 
growth, getting its food from the endosperm. At 
length it is able to push out a root into the soil, and much 
later it escapes wholly from seed and fruit and pushes up 
