360 
Journal of Agricultural Research voi. xxm, no 5 
dry matter. This increase doubtless is exaggerated in the averages 
due to the fact that all kernels are not equally advanced. 
The date of maturation of individual kernels is partially dependent 
upon minor features of location. Supposing that a kernel can not be 
rejuvenated after the percentage of water has fallen below 44 per cent, 
the time of reaching this percentage may be postponed by protection 
from the sun and air. The loss of water from the kernel is active on hot 
days. There is no loss at night during growth. Very hot, dry, sunny 
days may lower the water of exposed kernels near maturity below the 
point of recovery. Those kernels well covered by the awns of other 
kernels ripen slowly. The kernels on the under side of the spike of nod¬ 
ding varieties ripen after those on the upper side. In varieties like the 
White Smyrna, where several kernels are inclosed in the leaf sheath, the 
kernels so inclosed ripen much later than the exposed kernels. Pro¬ 
longed cool weather at ripening time must have a similar effect, and high 
yields of plump grain usually result from such ripening periods. These 
observations fit in with the appearance of the color in the Jet variety. 
While the amount of light reaching the kernel affects the intensity of the 
pigment and occasionally the time of its appearance, in general it affords 
an accurate index of the stage of maturity. 
SUMMARY 
In previous studies it has been shown that the average water content 
of the ovaries at flowering time is about 80 per cent and that the per¬ 
centage of water in the growing kernel decreases uniformly day by day 
until the average for all the kernels of a spike is about 42, when all deposit 
of dry matter is interrupted and the kernels dry with great rapidity. 
This 42 per cent does not represent the exact point where translocation 
of material becomes impossible but is lower than this point, as this is the 
average of all kernels on the spike and must include some with slightly 
more water which are still functioning and some with much less which 
ceased to function a day or two previously. 
Endosperm cells mature abruptly; the proteid content probably 
reaches a density beyond which it can not function. The Jet is a naked 
variety in which a black pigment is formed in the pericarp whenever this 
tissue ceases to be active. The appearance of color indicates that the 
first region to mature is on the dorsal surface near the tip. The region 
of the embryo on the dorsal surface is still later, and the cells adjacent to 
the furrow on the ventral surface are the last to mature. The first cells 
on the dorsal surface are affected when the moisture content of the kernel 
has reached 60 to 62 per cent. The kernels are fully mature when the 
water has fallen to 46 per cent and have carried on only a limited amount 
of translocation for some time. 
The date of final maturation can be postponed and the size of the 
kernel increased where kernels are protected by leaf sheaths or other 
shade and by cool weather at ripening. 
