34 BOTANICAL GAZETTE [july 



a mere glance. This characteristic behavior of cumarin-affected 

 plants becomes, therefore, in addition to the usual criteria, an 

 indicator of the degree of its harmfulness in the cultures of different 

 composition in this experiment. In addition to its effect on the 

 tops, as just described, there was a general inhibition of root growth, 

 as is the case with many other substances, notably the dihydroxy- 

 stearic acid already described. 



The effect of the cumarin was to depress the green weight of 

 the plants from ioo to 88 as an average in this experiment, although 

 it was obvious from the appearance of the cultures that its effect 

 was far from uniform in all of the cultures, and this is the most 

 interesting feature of the experiment. 



It will be recalled that with dihydroxystearic acid the more 

 normal growth was observed in the nitrogen end of the triangle, 

 but when the cumarin cultures were set out in this triangular form 

 according to the composition of the culture solutions, it became 

 at once apparent that the result with the cumarin was not in har- 

 mony with the observation so repeatedly made with the dihy- 

 droxystearic acid. It was clear that the cumarin had an entirely 

 different effect in the different culture solutions from that observed 

 in the case of dihydroxystearic acid, which had responded most in 

 the fertilizer combinations high in nitrate. With the cumarin 

 the growth was more nearly normal in the fertilizer combinations 

 high in phosphate. In comparing the cultures, those of like 

 composition only are compared in the cumarin and in the normal 



sets. 



nfluence of the phosphate on the harmful 



cumarin is perhaps most strikingly shown in the difference between 

 the plants growing in the culture solution containing no phosphate 



nam 



and 



mmediately above this, containing 



■tilizer mixture. Where phosphate 



the cumarin is most marked. Ab 



of the cumarin steadily decreases 



it, the 

 harm- 



the triangle disappears altogether, so far as the eye can detect 

 s in the appearance of the plants in the normal and cumarin set. 

 The effect of the phosphate in overcoming the harmful action 



