NO. 17 INHIBITION OF PLANT GROWTH — WEINTRAUB AND PRICE 7 



following the wood had been lowered to 3.5, however, indicating 

 absorption of an acid substance. 



When the air which had passed over the chips was scrubbed 

 through water its inhibitory potency was greatly diminished. Hence 

 the active constituent appears to be absorbed or destroyed by water. 

 Bubbling the air through 5N sulfuric acid did not remove the inhibitor. 

 These results also suggest that the active component may be acidic in 

 nature. 



Inhibitory effect of various volatile compounds. — While the above- 

 described experiments were in progress exploratory tests were made 

 with some of the substances which might be expected to be present, 

 in order to determine whether exposure of the seeds to the vapors 

 would result in inhibition similar to that produced by the emanations 

 from oils and wood. Volatile products of autoxidation of unsaturated 

 fats include carbon dioxide, carbon monoxide, organic acids, alde- 

 hydes, and peroxides, some of which have been shown to possess a 

 high degree of antibiotic activity. 



Carbon monoxide was tested at concentrations of i, 5, 10, 20, and 

 25 percent by volume in air. Retardation of germination and of root 

 and shoot growth occurred at concentrations of 10 percent and greater, 

 but even m 25-percent CO the inhibitory effect was much less pro- 

 nounced than that caused by the emanations from wood. 



For the hydrogen peroxide tests (pi. 7, fig. 2) the seeds were 

 placed in 3-liter jars containing open dishes of aqueous H2O2 solu- 

 tions (volume=:30 ml.; exposed surface=i25 cm.^). It is estimated 

 that air at 25° in equilibrium with 20, 50, and 90 percent solutions, 

 respectively, contains about 0.17, 0.29, and 2.25 mg. H2O2 vapor per 

 liter. 



Tests of the other compounds were conducted by placing small open 

 vials containing weighed amounts of the liquids, solids, or aqueous 

 solutions (in the case of formaldehyde and acrylic acid) in the desic- 

 cators with seeds. 



Sufficiently large dosages of several of the compounds were lethal. 

 At lower concentrations development was arrested but could be re- 

 sumed on subsequent ventilation, thus duplicating the effect of the 

 varnishes, oils, and wood. Continued inhibition without killing appears 

 to require a maintained supply of the vapor but the concentrations 

 necessary for this were not closely determined. It was, of course, pos- 

 sible to calculate the concentrations which would have existed if all 

 the introduced material were present as gas, but as some of the 

 compounds vaporized slowly and as there was, in all likelihood, loss 

 from the vapor phase by absorption, adsorption, or chemical reac- 



