212 
Journal of Agricultural Research 
Vol XXIII, No. 3 
A few Johnson grass caryopses had small, less resistant areas in the 
coat structures on the flat endosperm side opposite the embryo. The 
chromic acid, penetrating through these areas, ate small, deep holes into 
the endosperm. Such caryopses usually germinated if the integument 
over the embryo was still intact and the embryo itself uncolored by the 
acid. In fact even the starchy endosperm tissue, on account of its very 
hard, compact, glassy texture, seemed to be considerably more resistant 
to the corrosive action and to the penetration of the acid than was true of 
Sudan grass or wheat endosperms. 
Nearly all caryopses which germinated after treatment with chromic 
acid belonged to the first class shown in Table IV “apparently not 
affected. '' Of these nearly all produced strong vigorous seedlings when 
the length of the treatment did not exceed two days, with progressively 
weaker seedlings after longer treatments. All treated caryopses which 
germinated only after scratching produced very weak seedlings, while 
untreated caryopses which were brought to germination by scratching 
produced as vigorous seedlings as those which germinated without 
scratching. 
Microscopic examination of sections of the most resistant caryopses 
showed the inner integument and the closing tissue of the hilar orifice 
intact even after seven days treatment. Frequently the outer walls of 
the integument cells after more than two days' treatment were thoroughly 
disintegrated in places or so weakened and brittle that they broke away 
in sectioning, leaving only the thick inner walls covering the aleurone. 
All pericarp layers were present in places except after the very longest 
treatments, but these were greatly attacked at the hilar orifice, micropyle, 
and style, usually laying bare the closing tissue and sometimes also the 
micropyle within 24 hours. In most of the less resistant caryopses small 
portions of the integument were eaten away by the acid before coloring or 
disintegration of the underlying tissue began, but in a few of the less 
resistant and several of the more resistant caryopses there was evidences 
of local penetration of the acid sufficient to cause discoloration, through 
intact portions of the integument. The integument cells were on the 
average much more quickly destroyed over the embryo than elsewhere, 
so that after several days' treatment the embryo coverings in many 
caryopses were largely gone and the embryos themselves entirely gone, 
leaving at the proximal end of the caryopsis only the integument cells 
on the flat side and the closing tissue of the hilar orifice. From such 
caryopses were obtained the integument portions from which figures 8 
and 9 were drawn. 
RESISTANCE TO PENETRATION OP IODIN SOLUTION 
Brown, working with cereals (j) was the first to discover the existence 
of a nonliving, semi-permeable membrane surrounding any seed. He 
soon discovered (j, 4) that this membrane had selective qualities, allow¬ 
ing many solutes to pass through it readily, others only very slowly, and 
excluding still others. Schroeder (28) discovered a similar semi-permeable 
membrane in wheat grains, and showed that this membrane admitted 
both water and penetrant solutes mostly around the embryo and little if 
at all at the distal end of the grain. Collins (9) confirmed for barley 
Schroeder's result with wheat. His results led him to believe that the 
entry of both water and solutes took place almost wholly through the 
micropyle, which, however, he was unable to locate exactly. All of 
these authors agree that iodin passes through the selective permeable 
