74 BOTANICAL GAZETTE [February 



of compounds which occur naturally in plants. A few compounds 



which have not been found to occur as such in vegetable tissues are 



included in the study, for reasons which will be evident to the 

 reader. 



Material and methods 



The 



employed as water cultures for wheat seedlings. Most of the com- 

 pounds used were obtained from Merck & Co. and were used with- 

 out further purification. The water used in making up solutions 

 was shaken with washed carbon-black, allowed to stand thirty min- 



This 



TON (:o6), gives physiologically pure water. Continued use of the 

 method proves that it is as efficient in removing the toxic properties 

 of ordinar}' distilled water as careful redistillation in the presence 

 of strong oxidizing or reducmg agents. 



The solutions when made were placed in salt mouth glass bottles 

 having a capacity of 250^^, each of which accommodated ten seedling 



made 



million 



^y weight. Since electrolytic dissociation 

 pla\^ a very subordinate role in determining the toxic properties of 

 most organic compounds, the concentration of the solutions was 

 expressed in terms of the mass of the respective substance pres- 

 ent. Whenever nos^ihV \\^^ T,t'«.T.^of ._^^- ^^.,,.A ^rac 



1000 parts per million 



*'iooo 



ppm. ' A number of substances used were soluble only in amounts 

 less than looo ppm,; in these cases the range of concentration 



employed was much smaUer, and is noted in the last column of 

 Table 11. 



The wheat was ffermina 



mg 



23 and 40 of the Bureau of Soils. The 



entei^ 



fct true 



Lxum Its sneath. Iwenty plants in two cultures of ten each 

 were used in testing each concentration, and comparison was made 

 mth an equal number of plants growing in pure distiUed water under 

 like conditions. During the seasons of the year in which the condi- 



