1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 447 



KNO3 1.0 gm. 



MgSO, 05 



NaCl 5 



CaSO, 5 



FeCl^ 04 



Tap-water 1.0 liter 



No phosphate was included because of its precipitating action 

 on copper salts. After the cultures were about four weeks old 

 they were changed to nutrient solutions containing small 

 amounts of copper which was gradually increased from one to 

 ten parts per million of solution. The solution was neutralized 

 with normal H2SO4 (methyl orange indicator) to prevent pre- 

 cipitation of copper by dissolved carbonates. Following is a 

 summary of the history of the cultures, each of which was in- 

 creased to include several hundred plants: 



Wheat 

 Dec. 16 Planted in tap-water. 



Dec. 24 Transferred to nutrient solution, one-third strength. 

 Jan. 8 Changed to nutrient solution, two-thirds strength. 



Jan. 14 . To nutrient solution, full strength. 



Jan. 17 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. 



A faint biuret test appeared after addition of 6 p.p.m. Cu. Also dis- 

 tinct KiFeCje test. Eoots did not become flaccid, but the tops of cul- 

 tures were dying back and prostrated markedly in comparison with roots 

 of control culture. 



Canada Peas 



Dec. 20 Planted in tap-water. 



Dec. 30 Transferred to fresh tap-water. 



Jan. 6 Transferred to fresh tap-water. 



Jan. 18 Transferred to nutrient solution. 



Jan. 20 Changed 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. 



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



Feb. 6-8 Experiment terminated. 



A faint biuret test appeared after addition of 6 p.p.m. Cu. Distinct 

 K4FeCy6 test in root tips at end of experiment. Eoots not flaccid, but 

 plants distinctly affected and tops dying back more than those of control 

 culture. 



