127 
the Grain of Wheat ( Triticum vulgar e). 
cells was studied on 1907 material from Plot 10, Broadbalk, by means of 
series of hand-sections stained with iodine. It was afterwards found that 
grains from Plot 3 reached a similar stage of development about a day 
earlier, which is probably due to the fact that the heavy nitrogenous manuring 
of Plot 10 slightly retarded development. 
In all the younger stages there is a dense accumulation of starch in the 
pericarp, which gradually decreases in quantity, being utilized for respiration 
and possibly for the nourishment of the growing seed. Traces of this 
pericarp starch linger for a long time at the micropylar end, especially in 
the neighbourhood of the furrow. 
By the ninth day after pollination the endosperm is still incomplete, 
cell-walls only extending part of the way inwards from the periphery, while 
as yet there is no vestige of starch. 
Rapid progress is now made, for by the next day endosperm structure 
is nearly complete, except just in the middle of the tissue. Towards the 
lower end of the grain, one or two 
cells in the middle of the ‘ flanks ’ show 
minute starch grains in the closest con- 
nexion with the nuclei. Lower down 
rather more cells show this, but the 
starch all through remains very small 
and is only in association with the 
nuclei, never scattered throughout the 
cells. 
By the eleventh day from pol- 
lination the endosperm is completely 
formed and some starch is seen in the 
flanks well up towards the tip. The 
quantity in the flanks increases gradually as one goes down the grain, and 
though chiefly associated with the nuclei, the starch eventually begins to 
get scattered in the cells. At first there is no starch at all in the portion 
of the endosperm connecting the two flanks across the furrow, which we 
may call the e bridge \ Quite late in the series a little starch puts in its 
appearance across the bridge, but only in the cells on the side nearest to 
the furrow — none at all occurring on the outer side, except quite at the base 
of the grain. 
The next day, the twelfth from pollination, gives one of the most 
representative stages in the infilling of the starch in the endosperm. The 
embryo itself is still very small and little developed, and in its neighbourhood 
the endosperm, though quite complete, shows no sign of starch. A good 
deal of protein matter seems to be present, as a deep yellow coloration is 
obtained with iodine, both here and in most other series where the reaction 
is not masked by the deep staining of starch. Proceeding downwards 
Text-fig. i. Diagram to illustrate position 
of ‘ flanks ’ and ‘ bridge ’ in wheat endosperm. 
f flank ; b. bridge ; e?nb. embryo. 
