88 
Journal of Agricultural Research 
Vol. XXIII, No. 2 
EFFECTS OF MECHANICAL TREATMENTS 
I. WOUNDING 
Hiltner ( 21 ), Atterberg (6 ), and Kiessling (28) improved the germina¬ 
tion of various freshly harvested cereals by pricking or cutting the endo¬ 
sperms. Similar results were obtained by Zade (47) and by Atwood (7) 
with not after-ripened wild oats, by Harrington ( ig ) with not after-ripened 
Johnson grass seed, and by Andrews and Beals (j) with fully after-ripened 
maize. Hiltner (21) and Atterberg (< 5 ) combined the wounding treatment 
with presoaking, to which the results were in part attributed. Various 
interpretations of the favorable effects of the wounding have been put 
forward. 
In wild oats, Atwood (7) showed that the effect of the wounding is 
undoubtedly due to increased oxygen intake, oxygen deficiency being 
responsible for inability to germinate. Atwood’s results with cultivated 
oats also indicate that increased oxygen supply may be involved in the 
effect with oats. Hiltner ( 21) believed that the wounding increases 
germination by allowing imbibition of sufficient moisture, and others have 
spoken of enzymic activity being initiated by the admission of oxygen 
and the oxidative transformation of proteins. 
Kiessling ( 28) discredited all explanations of after-ripening which are 
based on coat exclusions. Since immediately closing the wounds with 
paraffine did not prevent the favorable effect of the wounding he believed 
that the effect of wounding is reached by exerting a “ stimulus ” upon the 
living protoplasm as in his interpretation of the effects of heat and cold 
on a stimulus basis. Behrens ( 8) came to the same conclusion, and 
Zade’s dissertation also includes some data which might be thought to 
favor the idea that the dormant embryo of w T ild oats is in a state of 
exceedingly delicate equilibrium and responds readily to mechanical 
shocks. But in the case of Zade’s work, it is probable that the rubbing 
of the embryo, which he interprets as causing mechanical stimulation of 
the embryo protoplasm, in reality increased the permeability of the coats 
to oxygen, thus supplying the increased amount of oxygen which Atwood 
later showed to be necessary. Furthermore, Kiessling’s stimulus 
hypothesis is difficult to accept on account of the mechanical obstructions 
in the path of conduction to the embryo of any wound stimulus exerted 
upon the endosperm. The only path through the medium of living cells 
seems to be by way of the aleurone layer, which has no organic union with 
the embryo. 
In the investigations herein reported two methods of wounding were 
adopted, both of which had been found to be very effective in causing 
the germination of dormant Johnson grass seed (19), namely, (1) cutting 
off the distal end of the grain just back of the embryo and germinating 
the embryo end alone, and (2) scratching the embryo itself along the entire 
length of one side of the scutellum by means of a bent dissecting needle. 
The axial organs were avoided, but the sdutellum was rather deeply 
wounded. Only a few lots were treated in either of these ways. 
When the distal ends were cut off and discarded the embryo ends of 
all lots of barley and oats and all but one lot of wheat so treated showed 
nearly complete germination at room temperature in from three to six 
days, but a marked tendency to decay after the treatment reduced the 
percentage of healthy seedlings from some unsterilized lots below T that 
for the controls. One lot of wheat showed 100 per cent germination in 
