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vestigated. A sprayed solution of common salt apparently acts likewise, 
first as a strongly plasmolyzing agent, but its action is even quicker than 
that of the sulphate, plasmolysis resulting even in from 10 to 15 minutes 
after the application of the spray. Wilting of the entire leaf soon follows, 
due to general withdrawal of water, to be succeeded in a few hours by 
the blackening of the protoplasm of the plasmolyzed cells. This blacken- 
ing is quite probably due to the formation of sulphides by the union of 
the absorbed iron sulphate with the protoplasm. After the use of common 
salt, on the other hand, the plasmolyzed spots turn reddish brown; possi- 
bly chlorides of some sort, formed in the killed protoplasm, may be re- 
sponsible for the color in this instance. 
It seems clear, then, that the action of the salts in killing the weeds 
in these experiments is due primarily to their osmotic properties rather 
than to their toxic properties; although it may well be that chemical action 
also may enter in after the first steps in the process and may contribute 
toward the death of the plants. 
One of the most interesting sides of the whole problem of spraying 
for weed destruction is the fact that while mustard, ragweed and most 
other common weeds are for the most part totally destroyed, the wheat, 
oats, flax, ete., are themselves but little injured. This sounds almost un- 
believable—much like a patent medicine advertisement, in fact. But it 
is nevertheless true that the grain soon recovers from the effects of the 
treatment; and further, Prof. Bolley’s statement seems true, that the 
sprayed field often yields as much as one-third more grain than the un- 
sprayed. 
A little examination of the sprayed field soon shows to what the 
grasses and grains owe their peculiar protection from serious injury. It 
is true that the tips of the young wheat leaves are blackened and killed; 
but it will be remembered that, when the plants are only six inches to a 
foot in height, the bases of most of the leaves are amply protected, en- 
wrapped within the sheaths and lower leaves. Their freedom from injury 
arises, therefore, in the main from the method of indeterminate growth 
of grains and grasses. The waxy bloom which covers flax and many of 
the grains must also contribute considerable protection against injury. 
since the minute droplets of salt solution do not adhere readily to such a 
surface. 
