Feb. 3.1923 Water Content of Barley Kernels During Growth 
359 
flowering—that is, the average kernel was affected by this date. On the 
curve of dry weight (fig. 10), it can be seen that the rate of increase fell 
off markedly on this date and never again reached the rate held consist¬ 
ently for a long period previously. The water content began to drop 
very rapidly at this time, as did also the wet weight. It seems without 
question that the abandonment of tissue began actively when the water 
content of the average kernel had reached 58 per cent. On some kernels 
this change evidently was initiated at 62 per cent. Dry matter was added, 
however, to other parts of the kernel for several days. Growth was 
essentially complete when the color had covered the ventral surface. 
This occurred when the kernel had reached 46 per cent of moisture and 
was common on all kernels when they had reached 42 per cent. This 
42 per cent coincides with the average date reported in various previous 
papers, and in this instance it is coincident with the average appearance 
of color. It would seem that, since 42 per cent represented the average 
water content when the spike was mature, this percentage would also 
represent the point at which the individual kernel should cease activity. 
That this is not true is due to the variation of spread before and after 
reaching maturity. Once a kernel has ceased active metabolism, the 
loss of water is very rapid and the spike average is lowered by wide range 
of water content in those kernels already mature. 
While not all kernels showed the appearance of black at the same 
time, the earliest kernels exhibited the color when a water content of 
about 62 per cent was reached. From the small spot first occurring the 
color gradually spread over the dorsal surface of the kernel. The base 
of the kernel was last affected on both the dorsal and ventral surfaces. 
On the ventral surface, color first appeared on the flanks of the grain 
from the center of the kernel toward the tip. The green in the pericarp 
disappeared last from the furrow of the kernel and naturally this is 
the last active tissue. Shortly after the black color appears on the dorsal 
surface, the kernel begins to dent—that is, the loss of water in this region 
is sufficiently rapid to cause the tissue to collapse. The loss of volume 
at this time is apparent in the measurements of the grain. The kernels 
of all varieties of barley contract as they lose water in maturing. In the 
Jet variety the kernel collapses in a depression on the dorsal surface 
which readies from the tip to the embryo. This is not common in barley 
varieties and doubtless comes about through the fact that in the Jet 
the tissues external to the nucellus are abnormally thickened in this 
region. Since such external tissues are not utilized for storage, the loss 
of water must be accompanied by an unusual reduction in volume. The 
final stage of ripening, or rather mechanical drying, is accompanied by 
a fine wrinkling of the entire surface of the kernel, as is common in other 
varieties. 
Assuming that the kernels of all varieties ripen in the same way as 
those of the Jet, the data here presented add this much to our previous 
information in maturation. The process of ripening is abrupt, as has 
been previously apparent, but this final stoppage of activity is the culmi¬ 
nation of a maturation which has already checked activity in some parts 
of the kernel. As may be seen in Figure 4, the drop in the average per¬ 
centage of water is not accelerated by the abandonment of the limited 
portion of the kernels first affected. It is only when the black spot 
becomes common, indicating an average condition of abandonment, 
that the rate of loss of water is accelerated and the rate of deposit of dry 
matter checked. From this time there is a slight increase in average 
25621—23-5 
