2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO7 



appeared to be initiated normally but, in most plants, ceased com- 

 pletely when the radicles and coleoptiles attained lengths of about a 

 millimeter. Seedlings in this arrested condition could be kept in the 

 chamber as long as 5 weeks without any apparent change. The inhibi- 

 tion was rapidly and completely terminated, however, by transferring 

 the plants to other containers constructed of glass, copper, galvanized 

 iron, or tin plate ; after such transfer the seedlings promptly resumed 

 development at a rate at least as great as normal. (See pi. i.) 



Preliminary tests with other species indicated that wheat and com 

 are affected very much like oats ; the germination of sorghum, barley, 

 tomato, bean, lettuce, and radish was also decreased or retarded, 

 but the inhibition was less pronounced than in the foregoing. 



In subsequent experiments with oats, described below, it proved 

 possible to achieve a greater degree of inhibition such that even the 

 incipient germination was suppressed. This suggests that the initial 

 development of seeds in the original growth chamber may have been 

 permitted by a lower concentration of inhibitor prevailing at the out- 

 set of an experiment, as opening the box necessarily permitted some 

 ventilation. 



The susceptibility of the seedlings decreases after the earliest stages 

 of development. Thus, seeds which were allowed to germinate for 2 

 days in a control chamber and were then transferred to the toxic box 

 exhibited relatively little subsequent retardation, whereas marked 

 inhibition resulted when the foreperiod was 24 hours or less. The 

 result of a similar experiment is shown in plate 2. 



Inhibition occurs both in light and in darkness, and on the silica 

 wicks either with or without filter paper. The effect was not found, 

 however, if the seeds were planted on soil or on an agar-water gel 

 (pl.3). 



SOURCE OF THE INHIBITORY EMANATION 



The materials of the growth chamber which could be implicated 

 as sources of the emanation were the varnish, the hardboard, and the 

 pine wood. 



Varnish. — The particular lot of varnish which had been used in 

 coating the original box was no longer available, but experiments were 

 made with five other brands from different manufacturers ; these were 

 tested as dried films on cardboard panels which were enclosed with 

 dishes of seeds in metal containers. All were found to retard seedling 

 development to some extent although in no case was the effect as 

 great as that originally observed. Similar results (pi. 4) were ob- 



