NO. 17 INHIBITION OF PLANT GROWTH — WEINTRAUB AND PRICE 9 



of hydrogen peroxide vapor, presumably as a result of oxidation of 

 some constituent of the effective materials, although some investiga- 

 tors have attributed it to emission of radiant energy. However, in view 

 of the relatively high concentration of hydrogen peroxide vapor re- 

 quired for inhibition of oats and of the negative test for this com- 

 pound in the wood aeration experiment, it is improbable that this is 

 the antibiotic agent. 



The mechanism of action on the plant is of particular interest in 

 view of the ready reversibility of inhibition. Continuous exposure to 

 the vapor is necessary in order that development remain arrested ; 

 there is no evidence of a cumulative effect on prolonged exposure at 

 the concentrations prevailing under the conditions employed. This 

 suggests that there may be a continuous absorption and detoxification 

 of the agent either by the plant or by the external water supply. It 

 is not known whether the vapor is absorbed directly by the seed or 

 must first be dissolved externally. 



In contrast to the emanations from wood, the vapors of certain of 

 the toxic chemicals which have been tested are not neutralized by 

 soil or agar (pi. 8). Possibly this difference is merely one of degree 

 and would not be found if the wood vapor could be supplied in 

 greater concentrations. 



That an effect so marked as the complete arrestment of develop- 

 ment has not frequently been noted by others who have cultured 

 seeds in small unventilated wooden or varnished containers may be 

 due to the detoxifying action of soil, and perhaps also of other or- 

 ganic materials used as substrates. The literature is not devoid of 

 references to more or less similar phenomena. Borriss (1940) pre- 

 sented evidence of the occurrence in air of germination-inhibiting sub- 

 stances whose action was nullified by the use of soil or charcoal as 

 substrate. He believed these vapors to arise, at least in part, from 

 the varnish of his incubators and showed that similar effects were 

 produced by emanations from turpentine, linseed oil, and varnish. 

 Raines (1935) reported that growth of roots was affected by vapors 

 liberated at room temperature from paraffine, "vaseline," mineral oils, 

 and various waxes, and Raines and Travis (1937) attributed seasonal 

 differences in root growth under uniform conditions of light and 

 temperature to ventilation conditions of the laboratory; it was sug- 

 gested that during the winter months the air contains higher concen- 

 trations of vapors from illuminating gas, paints, oils, varnishes, etc. 

 Possibly effects of this kind may have been involved in studies of 

 seasonal variations in seed germination (e.g., Schmidt, 1930; Baldwin, 

 1935)- 



