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90 
The Life of the Wheat Plant from Seed to Seed. 
from the underground parts of the plant to be finally stored in 
the seed, and necessarily iircreases the vr eight of dry matter in 
the plant abov’^e ground. 
VII. Ripening of the Grain. 
(I'hi-fijuns printed in the margin refer to the corresponding figures on page D8.) 
1 As soon as the ovule has been fertilised by the pollen-tube, 
active subdivision and increase of the cells take place, and the 
embryo is gradually developed. The stamens having done their 
work dry up and fall off, and the feathery styles wither and 
disappear. Hitherto the crude sap has been passing up the 
plant from the roots to the leaves; now the stored starch, con- 
verted, by the action of the protoplasm in the cells containing 
it, into grape sugar (glucose), is being sent from every part of 
the plant up to the seeds. A steady stream from leaf and stem 
4 and roots passes uji through cell after cell to supply the proto- 
5 plasm of the seed with material to build up the tissues of the 
0 little plant or to be stored up as starch for its future use. Day by 
3 day a steady enlargement of the seed goes on. The cells of the 
0 outer wall of the ovary are absorbed until it is gradually reduced 
1 1 to a single layer in the ripe grain. The covering that belongs 
14 to the seed itself, which is difficult to separate in the ripe seed, 
can be easily observed in these early stages. The fully developed 
7 embryo should be taken out of the seed and its difterent parts 
8 examined — the roots at the one end and the leaves at the other 
15 of the short stem, and the relatively large scutellum connecting 
the little plant with the store of food. When ripe every cell in 
the rest of the seed is packed with starch, and the protoplasm, 
which has followed the starch in its progress from all parts of 
the plant to the seed, is hardened into gluten for preservation 
and stored up by itself in the series of cells immediately under 
the skin of the grain, or scattered among the starch through the 
other cells. The entire store of food is called the endosperm. 
The whole life of the plant has been leading up to the pro- 
duction of these perfect seeds. From the time the first green leaf 
was expanded, the plant has been converting water and cai’bon 
and nitrogen into organic compounds, and building them up 
into its own structure or storing the surplus for use in this final 
work. The whole of this surplus material collected from every 
part is now stored up in the seed, and nothing remains in the 
plant but a skeleton of empty cell walls and dry woody fibres. 
The plant has done its work and dies — root and stock — leaving 
its numerous seeds each to reproduce an independent plant 
when the necessary conditions of heat and moisture are present. 
