84 



BOTANICAL GAZETTE 



[FEBRUARY 



of 500 and 250 ppm. the roots of the plants were entirely dead, although 

 the tops were still alive at the end of the experiment. Concentrations 

 of icx) ppm. stopped the growth of most of the plant roots and adven- 

 titious roots from the lower part of the stem ceased to grow as soon as 

 they dipped into the solution. Fifty ppm. was the lowest concen- 

 tration which appeared to cause injury to the plants. 



Hydrochinone (para-dioxybenzene) undergoes oxidation w^hen its 

 solution is exposed for some time to the air. True and Hunkel ('98) 



/ 



/ 



^ ). 





3.: 



\ 



fU? 



%- 



^ _ 



"t. 



fd 





■':r^ 





^- ■'■ 



■^\ . 



^ 





Fig. 3 



found that for lupine roots hydrochinone was more toxic than pyro- 

 catechin or resorcin. With wheat plants the order of results differed 

 somewhat, hydrochinone and p\Tocatechin appearing to possess toxi- 

 city of about equal intensity. In our experiments a concentration of 

 500 ppm. of hydrochinone was fatal, 25 ppm. caused injury, and 5 

 ppm. caused stimulation. 



Trlatomic ^/?eno/5.— Phloroglucin (1:3:5 trioxybenzene) is not 

 found as such in plants, but may be derived from several aromatic 

 plant constituents. It was found to suffer some oxidation when plant 

 roots were allowed to grow in its solutions, the stronger solutions show- 



