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 b}^ Harvey (11) of his own work on an alga 

 (Chlamydomonas multifilis) with that of True and Hunkel (30) on a 

 flowering plant (Lupinus albus), 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. 

 loOO 



When copper sulphate was used, Kahlenberg and True (14) found 

 that 0.00062 per cent was sufficient to kill the roots of Lupinus albus. 



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 many salts and acids 

 ver} T differently from seed plants and fungi. Bokorny (1) has re- 



