8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO7 



tion, the actual concentrations were probably considerably lower. 

 The special apparatus and technique required in order to maintain 

 known concentrations in the vapor phase for the 4- or 5 -day duration 

 of a test was not warranted in view of the lack of agent-specificity of 

 the inhibition. 



Of the compounds tested, the more active were: acrylic aldehyde 

 (acrolein) (see pi. 8), crotonaldehyde, hydrogen peroxide, crotonic 

 acid, and acrylic acid. Also effective, but at higher concentrations, 

 were: acetic acid, propionic acid, n-butyric acid, n-valeric acid, 

 n-butyraldehyde. At the vapor concentrations attainable, little or no 

 inhibition was produced by enanthic acid, caprylic acid, pelargonic 

 acid, capric acid, adipic acid, pimelic acid, or lauroyl peroxide. 



Owing to the nonspecificity of the inhibition, the value of these 

 exploratory tests with known compounds is of a negative character 

 in that they serve to eliminate as possibilities those substances found 

 to be relatively inactive but do not differentiate among the more 

 effective ones. 



DISCUSSION 



The foregoing observations raise numerous questions regarding the 

 nature of the volatile agent (or agents), the mechanism of its forma- 

 tion by diverse materials, the mode of its action on the plant, and 

 its detoxification by some substrates. Further experimentation is 

 required to provide the answers to these. 



It cannot be stated whether a variety of antibiotic agents is evolved 

 from varnishes, oils, unsaturated fat acids, and various species of 

 wood, or whether these diverse materials owe their activity to pro- 

 duction of a single compound. It seems unlikely that the agent is 

 present as such in these materials; rather it is probably formed 

 through oxidative processes. 



From the viewpoint of the inciting materials there is a degree of 

 similarity between the plant inhibition and the so-called "Russell 

 effect" by which is designated the production of a latent image in a 

 photographic emulsion in darkness by a large variety of materials, 

 including woods, resins, terpenes, animal and vegetable oils, and unsat- 

 urated fat acids (Russell, 1897, 1898, 1899, I904. 1906, 1908; Molisch, 

 1903 ; Schmidt, 1908; Kugelmass and McQuarrie, 1924, 1925 ; Baugh- 

 man and Jamieson, 1925; Haxthausen, 1925; Stutz et al., 1925; Kee- 

 nan, 1926; Mix, 1944). The agent responsible for this phenomenon 

 can act at a distance, be conducted through a bent tube, and penetrate 

 porous materials such as paper or gelatin but not glass or metals. 

 There is some evidence that the Russell effect is due to production 



