78 BOTANICAL GAZETTE [february 



waSj in some cases, a slight stimulation causing an increase in growth 

 over the controls. The physiological action of different samples of 

 tyrosin was found to var}^ somewhat. 



Upon long standing with exposure to air the tyrosin solutions 

 appeared to have undergone oxidation, all of them havuig become 

 quite dark in color. The changes wrought were probably the same 

 as those produced by the enzyme tyrosinase, which oxidizes tyrosin 

 to homogentisinic acid, which in turn gives rise to the dark-colored 

 compounds. 



An instructive result w^as obtained by studying the action of such a 

 t}Tosin solution which had suffered discoloration incident to age. 

 The tyrosin solution had become so dark in color that it resembled 

 manure extract. It was diluted so that it w^as equivalent to a i6 ppm. 

 solution of fresh t}Tosin. This solution was used for growing wheat 

 seedlings in comparison with a freshly prepared solution of tyrosin of 

 equal strength. 



^ Jbi a few days the plants in the two solutions sho^ved pronounced 

 differences, which became greater as the experiment was continued. 

 Fig. I shows the appearance of the plants when the experiment was 

 discontinued at the end of the twelfth day. The leaves w^re narrow 

 and beginning to die at the tips; the roots were dead and had become 

 sluny. The plants in the discolored t}Tosin had made excellent growth ; 

 they resembled plants grown in manure extracts. The leaves were 

 rich green, broad, and making vigorous growth, and the roots showed 

 a similar good development. During the course of the experiment 

 the ten plants in the fresh t>Tosin had transpired 19 grams of water, 

 and attained a green weight of 580 mffligrams. The plants in the 



tyrosin had in the same time 



These 



,ms 



vciiuc auu dcuon 01 me so-called green manures used in agricultural 

 practice. The extensive work of E. Schuxze and others has shown 

 that tyrosin and related compounds are quite widely distributed in 

 the vegetable kingdom. These substances may even increase in 

 number and amount when Yegetabie matter is aHowed to decompose 

 m the soil. Our experiments indicate that bodies like tyrosin 

 and cbrfm may have a toxic action uuon olants^ but that these 



