Brenchley , — The Development of the Grain of Barley. 925 
a coarse network structure. As the days go on these phenomena show 
a progression upwards, so that by the time the nuclei at the base of the 
grain have reached the coarse network stage, those a little higher up 
are getting deformed while those higher still no longer have nucleoli 
in evidence. The nuclei in the cells of the sub-aleuronic layer, and also 
those in the immediate neighbourhood of the furrow, do not begin to 
undergo any change for some time, but remain perfect. In ten or twelve 
days from the setting in of this 'nuclear senescence ’ 1 the flank nuclei are 
involved practically all through the grain, those at the base exhibiting net- 
works of a much finer structure. The nuclei under the aleurone layer have 
lost their nucleoli, but are still in a solid condition, except in rare cases 
in which slight deformation into coarse networks has begun. The nuclei 
round the top of the furrow are still all solid or even perfect, showing 
no deformation. Three days later great strides have been made, as at the 
base of the grain many cells of the sub-aleuronic layer show nuclei in the 
fine network stage, and all the way up the grain to the embryo such cells 
have either network or badly deformed nuclei. At the base, too, some of 
the cells round the ventral furrow have now been involved, showing sene- 
scence of nuclei to some degree, while the flank nuclei have continued 
to become finer in a regular progression upwards. In about three weeks 
from the time that the starch skeleton was first laid down practically all the 
nuclei of the endosperm cells up as far as the base of the embryo are 
involved in the senescence, though a few solid or deformed nuclei seem 
to hang on indefinitely, not developing into networks, especially round the 
furrow. 
While this progression upwards has been occurring in the lower part of 
the grain, similar changes have been taking place in the endosperm cells in 
the immediate neighbourhood of the embryo. The first nuclei involved are 
those in cells adjacent to the embryo, those further away from the embryo 
and those in the sub-aleuronic layer remaining perfect at first, except just at 
the point where the embryo abuts on the aleurone layer. The deformation 
appears to begin earliest at the tip of the embryo, proceeding downwards. 
The senescence spreads rapidly outwards through the flanks and bridge, 
until all cells are involved save those of the sub-aleuronic layer and those 
round the furrow. By the tenth or twelfth day from the beginning of the 
senescence most of the nuclei at the level of the embryo are deformed 
or are dense networks (except just under the outer aleurone layer), especially 
in the deeper seated flank cells and across the bridge. Towards the base 
of the embryo at this date a few cells in the sub-aleuronic layer show dense 
networks, though the nuclei round the top of the furrow are still perfect. 
Three days later, when most of the flank nuclei in the lower part of the 
1 See Brown, H. T., and Escombe, F. : Proc. Roy. Soc., vol. Ixiii, No. 389, 1898, p. 18; also 
Trans. Guiness Research Lab., pp. 123-7. 
