6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, IO7 



In several experiments in closed vessels containing pieces of wood, 

 a curious effect was noted. In a single population of seeds planted 

 on a silica block of relatively small dimensions, some plants might be 

 inhibited much more than others, but the variation was not distributed 

 randomly through the population as would be expected if it were due 

 to individual differences in susceptibility; rather a positional effect 

 was manifest. That is, plants at one end of the wick might be com- 

 pletely checked while the growth of those at the other end would be 

 only slightly retarded ; the seedlings between exhibited an intermediate 

 response. Examples of this behavior are illustrated in plates 2 and 5. 



The explanation seems to be that the active vapor is not distributed 

 uniformly in the air of the container. The combined influence of the 

 slow diffusion within a closed vessel maintained at uniform tempera- 

 ture and the relatively rapid removal of the agent from the vapor 

 phase results in concentration gradients within the confined space. 

 To test this hypothesis, two wicks were arranged end to end in a 

 jar and some pieces of board were placed near one end of one of 

 the wicks. A rather striking gradation of inhibition, according to the 

 distance from the wood, resulted (pi. 7, fig. i). Similar effects are 

 produced also by vapors of known chemicals if the locus of produc- 

 tion of the vapor is situated unsymmetrically with respect to the 

 seeds. This was shown unmistakably by seeds exposed to hydrogen 

 peroxide vapor although not so clearly evident in the reproduced 

 photograph (pi. 7, fig. 2) ; in this experiment, each dish of seeds was 

 in an individual jar with dishes of hydrogen peroxide solution ad- 

 jacent to the ends of the wicks shown at the right-hand side of the 

 photograph. 



Tests on vapor from wood. — Room air was humidified and drawn, 

 by means of a water-line aspirator, through a glass tube (4 m. long, 

 4 cm. diameter) packed with 350 g. of spruce chips. At a flow rate of 

 approximately 15 1. per hour this air completely checked the develop- 

 ment of oat seeds when passed through a desiccator in which they 

 had been planted. A similar set of seeds placed in the air stream 

 ahead of the wood was not inhibited showing that the unaltered room 

 air was nontoxic. 



The desiccators were then replaced with gas washing bottles con- 

 taining 100 ml. of boiled distilled water (pH = 7.o) through which 

 the air was passed as fine bubbles during a 5-day period. At the end 

 of this time the water was found to be free of ammonia ( <o.oi mg.), 

 hydrogen peroxide (<o.i mg.), and substances capable of oxidizing 

 potassium iodide in acid solution. The pH of the water in the bottle 



