201 
jan. 20,1923 Structure 0} the Pericarp of Johnson Grass Seed 
tective cover to the large hilar opening through the inner integument. 
This cover we have designated as the “closing tissue” of the hilar orifice. 
As will be shown later, it is largely , impervious to solutes and highly 
resistant to the action of 50 per cent chromic acid. In its protective 
function it supplements the inner integument with which it is struc¬ 
turally united through the fusion of the respective cell walls. Its intense 
pigment, showing through the overlying layers of pericarp cells, forms a 
circular black area which is always conspicuous in an external examina¬ 
tion of the entire caryopsis. Around this closing tissue in all directions 
the degree of pigmentation abruptly decreases, though there is no sharp 
line between the very dark central region and the surrounding cells. In 
fact, when completely bleached with Javelle water, the cells of this dark 
central region and those above and below it are almost identical in 
Fig. 7. —Median transverse section through the hilar orifice of a Johnson grass caryopsis: a, a, inner integu¬ 
ment; b, b, compact group of thick-walled pericarp cells; c, “closing tissue’' of the hilar orifice; d, outer 
^epidermis of the pericarp; e. pericarp cells completely filling the hilar orifice in the integument. X 275. 
appearance. The pericarp cells (e) within the margins of the hilar orifice 
are roughly cubical in shape and are arranged rather regularly in radial 
rows. In the absence of vascular bundle elements it is obvious that this 
mass of tissue—completely filling the hilar opening through the integu¬ 
ment, and parenchymatous until pigmentation sets in during the matura¬ 
tion and drying of the caryopsis—acts as the only avenue for the con¬ 
duction of nutrient materials from the vascular elements at the base of 
the pedicel and over the hilar region to the developing embryo and 
endosperm. Rows of long, thin-walled cells in the central layers of the 
pericarp tissue leading from the coiled branch of the vascular bundle of 
the pedicel and continuous with rows of cells within the hilar opening, 
doubtless also function as conducting elements. In the mature un¬ 
bleached caryospis, however, the dark central portion is strikingly 
differentiated from the surrounding structures. Moreover, the contrast 
here existing is accentuated by partial bleaching of microtome sections 
