jan. 30 ,1933 Structure of the Pericarp of Johnson Grass Seed 
211 
Table IV .—Resistance of the coverings of Johnson grass caryopses to the action of 50 
per cent chromic acid —Continued 
Seed lot from San Antonio, 1916. 
Condition of caryopses: 
Apparently not affected, or slightly 
darkened or mottled over embryo... 
Portions of embryo or its coverings 
(especially axial organs) more or less 
darkened or many after more than 1 
or 2 days’treatment with part of em¬ 
bryo eaten away. 
Parts of endosperm eaten away through 
weak place in covering on flat side, 
usually opposite the embryo. 
Germination percentage at 26° C.: 
1 day. 
2 days. 
3 days. 
Total germination after unscratched 
period 3 4 . 
3 days 2 . 
4 days 2 . 
6 days 2 . 
Total viable. 
Effect of varying length (days) of treatment with 
chromic acid. 
Per ct. 
44 
19 
o 
63 
36 
o 
99 
Per ct. 
73 
26 
60 
12 
o 
72 
75 
Per ct. 
50 
50 
40 
5 
1 
46 
46 
Per ct. 
24 
76 
12 
IO 
26 
Per ct. 
7 
93 
Perct. 
1 The different lots are arranged in the order of increasing difficulty of germination, especially before 
after-ripening. 
8 Embryos scratched at end of second or third day with a bent needle to induce germination. 
Table IV shows the main features of the result with Johnson grass 
caryopses. These were remarkably resistant to the action of the chromic 
acid. The following points deserve special mention: 
1. The resistance of the different lots to the action of the acid increased 
with increasing difficulty of germination, the readiest germinator (No. 
37001) being most rapidly attacked by the acid and the poorest germinator 
(San Antonio, 1916) being most resistant. 
2. The action of the acid for 24 hours or a longer period so reduced the 
resistance of the coat structures that practically all the embryos which 
were still viable germinated in 2 or 3 days without “scratching” whereas 
about 40 per cent of the controls failed to germinate until after scratch¬ 
ing. In the most resistant lot (San Antonio, 1916) the percentage which 
germinated without scratching was actually increased by 24 hours * 1 treat¬ 
ment. This recalls the action of concentrated sulphuric acid in removing 
the embryo coverings and thus inducing prompt and complete germination 
(r 5). In the case of the chromic acid the least resistant caryopses were 
killed within the first 24 hours, but a larger number of the most resistant 
caryopses were rendered easily germinable by the action of the acid. 
3. The percentage of viable caryopses, and after the first 24 hours the 
percentage which germinated without scratching, decreased progres¬ 
sively with increased length of time in the chromic-acid solution. 
4. In contrast to wheat and Sudan grass caryopses, which were killed 
within 24 hours, a small percentage of Johnson caryopses were still viable 
after 5 to 7 days. 
