4 BULLETIN" 227, U. S. DEPARTMENT OF AGRICULTURE. 
Seed plants. — A great amount of work has been done to ascertain 
the effect of various toxic substances on the roots of higher plants. 
A discussion of this work, however, is not essential to the present 
paper beyond showing that a considerable difference exists between 
the behavior of this group of plants as compared with the lower 
forms. 
In the comparison by Harvey (11) of his own work on an alga 
(CJilamydomonas multifilis) with that of True and Hunkel (30) on a 
flowering plant {Lupinus alius), both investigators using the ortho, 
meta, and para compounds of dihydric phenol, cresol, and phthalic 
acid, the alga was found to withstand a concentration three to eight 
times as high as the flowering plant. 
Another striking illustration of this varied response to the same 
toxic solution is recorded by Heald (12, p. 130), who found a fungus 
vigorously growing on pea roots which had been killed by hydro- 
chloric acid. The average death point for five species of molds 
studied by Clark (3, p. 306) was-^HCl (1.1 per cent), while the 
three species of flowering plants investigated by Heald (12, p. 132) 
succumbed at -„„„ HC1 or less. 
loUU 
When copper sulphate was used, Kahlenberg and True (14) found 
that 0.00062 per cent was sufficient to kill the roots of Lupinus dlbus. 
After many experiments, Clark (3, p. 396) concludes that in the 
case of mineral acids a concentration of 2 to 400 times the strength 
fatal to the higher plants is required to inhibit the germination of 
mold spores under favorable conditions. 
Bacteria. — Although no direct comparison of bactericidal and 
fungicidal action is available, the experiments being usually per- 
formed under somewhat different cultural conditions, the work of 
McClintic (17) on zinc chlorid indicates a high resistance of certain 
bacterial organisms. This investigator found that a 5 per cent 
solution of zinc chlorid applied for one hour was not sufficient to kill 
Bacillus communis, while a 25 per cent solution required 10 minutes 
to cause death. At this latter concentration 30 minutes was re- 
quired to kill another bacterial organism {Staphylococcus pyogenes 
aureus) . 
Spores of bacteria are well known to be very resistant to various 
agents. In the case of Bacillus subtilis, they are reported to have 
survived a 50 per cent solution of zinc chlorid for 40 days. 
These figures are of interest when one recalls that a 3 to 6 per cent 
solution of this salt is the usual concentration employed in the 
preservation of wood. 
Yeasts. — Yeasts seem to behave toward man}' salts and acids 
very differently from seed plants and fungi. Bokorny (1) has re- 
