Apr. is, 1921 
Susceptibility of Injured Seeds to Molds 
109 
Reichard (16, 17) did not find barley seed coats so perfectly semiper- 
meable as those Brown described, and he attributes such variations to 
differences in the tannin content of the testa. He believes that solu¬ 
bility or nonsolubility of this tannin in the external solution determines 
the latter’s penetrability. Differences in the tannin content of the active 
cells occur as the result of differences in the ripening process, he thinks, 
unripe seeds being more permeable because the tannin has not been fully 
deposited. It is interesting in this connection to note Falke’s (8) con¬ 
clusions as to the cause of the poor stand of wheat obtained from seed 
grown in an abnormally dry season. Not only was the wheat from un¬ 
treated seed grown that year less vigorous, but when the seed was treated 
with a 0.5 per cent solution of copper sulphate it was extremely injured, 
while seed of the same varieties grown the preceding year showed much 
less effect of the poison. He concludes that the dryness of the season 
had affected the development of the testa with the result that it was 
more permeable to the>poison. In all tests seeds with unbroken coats 
were selected for treatment. 
In his studies on the semipermeability of the seed coats of wheat and 
barley, Schroeder ( 18 , 19) also found them to be impermeable to copper 
sulphate. Shull ( 20) thinks it reasonably certain that copper sulphate 
does not penetrate a sound testa. He attributes exceptions to defects 
in the seed coat too slight to be seen even on microscopic examination. 
Crocker and Davis (6) found that Alisma seeds would withstand a 
molecular copper-sulphate solution for a month. 
These researches on the permeability of seed coats are comparatively 
recent, but it was known in 1872 that the injury to wheat resulting 
from treatment with copper sulphate was dependent on the physical 
condition of the seed coat. Nobbe (15) first recognized the fact that 
machine-thrashed seed was more injured by copper sulphate than was 
hand-thrashed seed, because damage done, to the seed coats by the 
machine allowed the copper sulphate to penetrate to the embryo. He 
pointed out that the drier and more brittle the crop, the greater the 
thrashing injury. With the visibly injured kernels removed from the 
sample, he found germination to be as good as that of the hand-thrashed 
sample. 
Kuhn ( 14 ) reported no injury from copper sulphate when he used 
hand-thrashed wheat. Grassman (10) used machine-thrashed seed 
because it was what the farmers had to use, but he recognized the cause 
of the injury sustained by it and recommended that if in practice machine- 
thrashed seed had to be used, the strength of the copper-sulphate solu¬ 
tion should be reduced. Falke (7) noted more treatment injury to 
machine-thrashed than to flail-thrashed grain. Von Tubeuf (21) found 
that machine-thrashed wheat would not stand treatment which was 
harmless to hand-thrashed grain. He, however, notes varying degrees 
of injury to hand-thrashed seed soaked 18 hours in a 2 per cent copper- 
