jan. so, i 9 2 3 Structure of the Pericarp of Johnson Grass Seed 
207 
Caryopses of Sudan grass and Johnson grass No. 37001 became almost 
black in one-half hour, and those of the San Antonio lot in an hour. 
The initial blackening was followed by gradual bleaching, which was 
first apparent and proceeded most rapidly over the embryos and thence 
advanced around the endosperm at the proximal end, and at the same 
time toward the distal end over the entire circumference of the caryopsis. 
As the seeds whitened the bleaching solution darkened. More rapid loss 
of color in spots frequently gave a mottled appearance to the bleaching 
caryopses. The closing tissue of the hilar orifice and the inner walls of 
the very large integument cells at the distal end of the caryopses were 
the slowest to show the effect of the bleaching and the last to become 
completely bleached. Often the circular closing tissue of the hilum re¬ 
mained very dark 24 hours after all other tissue at the proximal end of 
the caryopsis was completely bleached. 
In many Johnson grass caryopses the coverings over the edges of the 
scutellum and over the axial organs bleached more quickly than a little 
to either side of the axis, leaving two prominent dark lines the whole 
length of the embryo after the rest was white. 
Table III shows in detail the progress of bleaching in the three lots 
of caryopses and the results of germination tests of the same lots of 
caryopses. The germination tests were made in 100 mm. Petri dishes 
with wet blotting paper as germination bed. Sudan grass was tested 
at room temperature and Johnson grass in an incubator at 26° C. 
Examination of the data in Table III shows that Sudan grass caryopses 
bleached much more rapidly than Johnson grass caryopses and Johnson 
grass No. 37001 more rapidly than the San Antonio lot. Correlated 
with the difference in resistance of the two lots of Johnson grass 
caryopses to the action of Javelle water was a difference in the 
readiness with which they germinated. This latter difference, while 
only slight in the fully after-ripened condition at the time these 
tests were made, was, as previously indicated, very much greater 
when the seeds were fresh. Viability tests made after the third day 
by scratching the embryos along one side of the scutellum with a bent 
needle and returning them to the incubator for another day showed 
all the caryopses to be viable and capable of producing vigorous seedlings. 
The application of this method of determining the viability of Johnson 
grass embryos has been described elsewhere (15). 
A few of the most resistant Sudan grass caryopses bleached more slowly 
than a few of the least resistant Johnson grass caryopses. It is perhaps 
worthy of notice also in this connection that 1 per cent of the Sudan 
grass caryopses, though viable and potentially vigorous, did not germi¬ 
nate until after the coverings of the embryo had been opened—a process 
which induces the germination of the most resistant Johnson grass 
caryopses even before they have after-ripened. 
Additional bleaching tests were made with the San Antonio lot of 
Johnson grass, using caryopses which had failed to germinate in three 
days at 26° C. in comparison with others which had for three days been 
incubated as for germination except that germination was prevented by 
keeping them in an ice box. The caryopses remaining from the germi¬ 
nation test bleached on the average more slowly than those which had 
been incubated in the ice box, so that none germinated. This seems 
to indicate that the caryopses of this lot which had germinated were 
in general those which would have bleached most rapidly in Javelle 
water. 
