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. 



