20 BULLETIN 1239. U. S. DEPARTMENT OF AGRICULTURE. 
Infection from infested soil can be considerably reduced by in- 
crusting the seed with a soluble fungicide and sowing no deeper than 
is required by soil-moisture conditions. The degree of such pro- 
tection may be profoundly affected by the temperature and moisture 
conditions of the soil, the optimum conditions consisting in a tem- 
perature of approximately 18° C. (64° F.), soil in good tilth, and 
low atmospheric humidity. Such conditions would promote prompt 
germination of the grain and an upward flow of the dissolving toxin 
by. capillary action; while the most unfavorable conditions would 
result from a combination of soil temperature sufficiently low to 
cause slow germination of the seed and a wet, poorly aerated soil, 
which would cause the toxins to percolate downward. 
In this connection, threshing damage to the seed coat of the wheat, 
which increases its susceptibility to injury from copper-sulphate 
treatment, is of importance. Experiments by Nobbe (17), Grassman 
(10), Falke (7), and Tubeuf (22) established the relation of seed- 
coat injury to loss of viability after treatment with copper sulphate. 
Falke (8) found a great difference in the germinative power of wheat 
of the 1903 and 1904 harvests after treatment with CuS0 4 . Even 
after sorting out all visibly injured grains a considerable difference 
was manifest. The crop season of 1904 was an exceptionally dry 
one, and Falke believed this condition to cause the seed coat to be 
more permeable and more easily injured. 
Volkart (24) found hand-threshed wheat immune from injury by 
copper sulphate when immersed 14 hours in a 0.5 per cent solution, 
while machine-threshed seed treated in the same manner was almost 
entirely killed. He also found that a four-hour treatment in a 0.1 
per cent solution of formaldehyde killed a large part of the machine- 
threshed seed, while the hand-threshed seed was uninjured except 
that its germination was slightly delayed and the seedling growth 
retarded. 
Brown (5) found the testa of wheat, barley, and oats to contain a 
semipermeable or selective membrane; this, while admitting water 
freely, excluded sulphuric acid and certain salts, among which were 
copper sulphate and silver nitrate. Schroeder (19) confirmed Brown 
and found further that the membrane was permeable to an aqueous 
solution of mercuric chlorid and to chloroform. The work of Shull 
(20) in 1913, directed principally toward an explanation of the 
phenomena along physical and physiological lines, developed no 
further facts related to the immediate problem of seed treatment. 
In the Northwest the injury to wheat from threshing was found to 
be excessive. The reasons for this are (1) that it is almost always 
threshed very dry, the atmospheric humidity in these regions being 
extremely low during July, August, and early September; and (2) 
threshing machines are run at very high speed. It is not unusual to 
find 10 per rent of the kernels of a lot of wheal split in halves. Field 
observations and laboratory experiments showed thai an immense 
amount of seed was being Inst through treatment with copper sul- 
phate in consequence of tnis threshing injury. An investigation of 
this problem was reported by Wbolman (25). These studies showed 
that the point, where copper-sulphate solution is the most deadly 
Is i lie hilar membrane covering the extremely susceptible radicle, 
where breaks in the lest.i of the seed are most Likely to oeenr. A 
