Physiological Observations 197 



Corn 



Dec. 22 Planted in tap-water. 



Jan. 8 Changed to nutrient solution, one-tliird strength. 



Jan. 19 To nutrient solution containing 1 part Cu per million. 



Jan. 21 To nutrient solution containing 2 parts Cu per million. 



Jan. 25 To nutrient solution containing 6 parts Cu per million. 



Jan. 28 To nutrient solution containing 10 parts Cu per million. 



Feb. 9 Experiment terminated. 



Giving distinct, faint biuret test after addition of 6 p. p.m. Cu; also 

 KiFeCjs test at end of experiment. Eoots not flaccid at end of experi- 

 ment, but tops of cultures about half dead, while tops of control culture 

 were still in good condition. 



These cultures, as shown by the notes, were exposed to cop- 

 per solutions — wheat twenty-three d^ys, peas eighteen days, 

 corn twenty-one days. At the end of the experiment roots were 

 not flaccid, but very faint biuret and distinct ferrocyanide tests 

 were observed. In all cases top growth was affected, corn most, 

 wheat next, and peas least. This material, as indicated above, 

 is poisoned only just enough to show reactions in root tips, 

 although tops are distinctly affected. It, therefore, represents 

 minimum rather than maximum toxic conditions. Material was 

 harvested and analyzed to show copper and nitrogen ratios; 

 and by estimating the number of root tips in samples of corn, 

 peas, and wheat the amount of copper per root tip, required to 

 show faint tests, was found. 



TABLE XXVIII 



Quantitative Determinations on Water Cultures Showing Slight 



Toxic Effects 



Corn 



Amount of copper per root tip associated with slight toxic effects, 

 .00042 -^ 1100 = .000000382 gm. 



