209 
jan. 20,1923 Structure 0} the Pericarp of Johnson Grass Seed 
The first treatments were with halved caryopses of three lots of fully 
after-ripened Johnson grass seed showing 100 per cent viability in com¬ 
parison with halved caryopses of dark-colored and light-colored Sudan 
grass seeds. The caryopses, either in air-dry condition or after soaking 
in water, were cut in halves along a median sagittal plane with a sharp 
scalpel and were then immersed in 50 per cent chromic-acid solution, 
which was frequently changed. At the end of 24 hours’ soaking in the 
chromic-acid solution some of the halved caryopses were washed in water 
and examined with the microscope. At this time considerable endo¬ 
sperm, white and normal in appearance, remained within the half-shells, 
but the majority of the embryos were entirely disintegrated. The cover¬ 
ings over the Sudan grass embryos were very considerably fragmented, 
and in most cases the remaining tissue was fragile and soft and tended to 
collapse into the empty embryo cavity. In the great majority of the 
Johnson grass half caryopses, on the contrary, the shells over the embryo 
cavity were intact or only slightly fragmented and remained stiff and 
brittle. Many of these were kept several days longer in 50 per cent 
chromic-acid solution without undergoing entire dissolution of the 
enbryo coverings. Embryo coverings of caryopses of the Johnson grass 
lot which was most resistant to germination, especially before after¬ 
ripening, were more resistant to the action of the chromic-acid solution 
than embryo coverings of the other two lots. 
Entire caryopses of these same lots of Johnson grass and Sudan grass 
and wheat grains from a lot showing 99 per cent germination in two days 
were next treated with 50 per cent chromic-acid solution in small vials 
each containing 100 caryopses. At 24-hour intervals the caryopses in 
the different vials were removed from the chromic-acid solution, thor¬ 
oughly washed with sodium-bicarbonate solution followed by distilled 
water, and put to germinate. At the same intervals caryopses were 
withdrawn from another vial of chromic-acid solution for sectioning 
and microscopic examination. 
All wheat embryos were uncovered and killed by the action of the 
chromic acid by the end of the first 24-hour period, though in the most 
resistant grains scutella and the larger part of the axial organs were 
still intact. Fragments of the outer coverings, sometimes including 
even the outer epidermis of the pericarp, remained. 
With Sudan grass caryopses only the inner integument and the closing 
tissue of the most resistant individuals remained intact at the end of 24 
hours’ treatment. Occasional adhering remains of the outer coverings 
usually represented only the inner epidermis of the pericarp. The whole 
proximal end, both embryo and endosperm, tended to become slightly 
stained, showing the slight penetration of the acid. Only 1 per cent of 
the embryos of dark-colored caryopses were very weakly viable after 24 
hours in the chromic-acid solution. Sixty-seven per cent of the embryos 
of dark-colored caryopses were wholly or partly disintegrated, while the 
other 33 per cent were not yet exposed by the disintegration of the inner 
integument. Eight-colored caryopses were much less resistant than 
dark-colored caryopses, all embryos being more or less disintegrated and 
only a small distal portion of the endosperm remaining intact in several 
caryopses. 
