NO. 17 INHIBITION OF PLANT GROWTH WEINTRAUB AND PRICE 3 



tained with films prepared from various vegetable oils (linseed, soy- 

 bean, safflower, and castor) containing lead and cobalt naphthenates 

 as driers. A layer of linoleic acid also was found to cause some re- 

 tardation of growth ; its effectiveness could be increased by ex- 

 posure, in an open dish, to daylight for several hours prior to the 

 test. Oleic acid, which is less unsaturated than linoleic, had very 

 little inhibitory activity. 



These tests indicated that varnishes, vegetable oils, and unsatu- 

 rated fatty acids give rise to emanations which retard seedling de- 

 velopment.* However, the effects observed were less marked than 

 those found in the toxic growth chamber, and while the possibility 

 was considered that the difference might be due to more rapid pro- 

 duction of the active agent from the original varnish, it seemed de- 

 sirable to make further tests of the other materials of the box. 



Wood. — Accordingly the varnish was removed mechanically from 

 the box with a cabinet scraper ; the inhibitory activity was not dimin- 

 ished thereby but rather seemed to be somewhat enhanced. A second 

 box was then built entirely of pine boards (not certainly identified 

 as to species but belonging to the yellow-pine group) which had 

 never been varnished; in this box the inhibition was unmistakably 

 greater than in the first, germination being completely suppressed. 



An experiment was next set up in which lo other species of wood 

 were tested in the form of small pieces of well-seasoned board in 

 desiccators or bell jars. All proved to exert a marked inhibitory action 



(pl. 5). 



All these tests were essentially qualitative, the appearance of the 

 seeds or seedlings being deemed a sufficient criterion of the occurrence 

 of inhibition. It was not thought worth while to attempt to develop 

 a more quantitative measure of inhibition until the factors influencing 

 production and action of the inhibitor were better understood. Fur- 

 thermore, as the wood samples employed in the previously described 

 experiment were obtained from scraps of lumber of uncertain history, 

 scant significance would appear to attach to the relative effectiveness 

 of the different woods. What relation may exist between the amount 

 of wood present and the magnitude of the inhibition has not been as- 

 certained. Data on weights, volumes, and surfaces of the samples used 

 are presented in table i . 



* On the basis of our previous experience with culture of oat seedlings we 

 can conclude that the decrease in oxygen content and increase in carbon diox- 

 ide content of the atmosphere (which accompany autoxidation of drying oils 

 and unsaturated fatty acids in closed containers) were much too small, under 

 the existing conditions, to have been of significance as factors in the inhibitory 

 action. 



