THE TOXICITY TO FUNGI OF VARIOUS OILS AND SALTS. 35 
gelatin media, even when the tests are conducted under exactly 
similar conditions, do not necessarily represent the true relative 
toxic values of the different compounds, for the interaction between 
the toxic compounds, the nutrient substances contained in the 
media, and the plant protoplasm is variable and more or less specific 
for each combination. 
Also, the reader should keep before him the fact that toxicity alone 
is not the sole criterion in judging the service value of a preservative, 
and a direct application of these data to that end would in many 
cases lead to very erroneous conclusions. 
In many cases it is possible to overcome such unfavorable proper- 
ties in a preservative as high solubility in water by placing the treated 
timber under conditions less exposed, and such timbers treated with 
soluble preservatives, such as sodium fluorid, zinc chlorid, and copper 
sulphate, should behave more or less according to the toxic ratios 
represented. The same should apply to oils of similar volatile and 
soluble properties placed under approximately similar service con- 
ditions. 
Not all preservatives are adapted to the same uses, and in testing 
their service value these primary facts should be given full consider- 
ation. We have long been in the habit of taking as the standard 
test of the efficiency of a substance its ability to protect timber 
exposed to such extreme conditions as are railway ties, telephone 
poles, posts, exterior building timbers, etc. This standard is very 
often too severe, and for this reason preservatives should be grouped 
according to the conditions under which they are to be exposed. 
SUMMARY. 
A survey of the work of various investigators on the action of 
different toxic substances on the higher and lower forms of plant life 
discloses a marked difference in behavior. The action of toxic agents 
appears to be specific, being highly poisonous to certain organisms 
and only moderately so to others. 
Very dilute concentrations ordinarily produce a stimulative effect. 
Among the fungi, as a rule, the common molds are more resistant 
to poisons than the true wood-destroying fungi, and even among the 
latter group the different species show a great difference in suscepti- 
bility. 
The chemical and physical composition of the media supporting 
the growth of the fungi determines, to a large extent, their develop- 
ment. The presence of certain kinds of insoluble matter or of such 
organic compounds as sugars and proteid materials, with which the 
toxic agents may possibly react, often introduces a considerable 
element of error when testing the toxic value of a substance by 
mixing it with nutrient agar or gelatin media. 
