1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 467 



In this statement, for instance, field samples of corn roots 

 grown in soil containing 0.07 per cent of copper contained only 

 42 p. p.m. of copper in dry matter, while a plot sample grown in 

 soil containing .025 per cent of copper contained 245 p. p.m. of 

 copper in dry matter, and corn grown in pot culture containing 

 0.02 per cent of copper in soil contained 748 p. p.m. of copper in 

 dry matter. 



These differences may be due to the coarser root systems of 

 plot and field-grown samples, this condition being associated with 

 relatively small amounts of copper in dry matter. In view of the 

 great labor involved in preparing root samples for analysis and 

 the very variable results obtained from copper determinations 

 made upon such inaterial, there seems to be little hope of estab- 

 lishing satisfactory ratios of copper to dry matter for the pur- 

 pose of determining that a sample of field material has been 

 injured b}" copper. It is probable, however, that for comparative 

 purposes, pot cultures of field soils conducted under uniform 

 and carefully regulated conditions, with standard plants of 

 known behavior, may yield figures of comparative value in de- 

 termining the character, toxic or otherwise, of a soil containing 

 copper. Corn is an excellent summer-growing plant for the pur- 

 pose, inasmuch as it shows toxic effects easily, grows rapidly, and 

 affords abundant root materials for analytical determinations. 

 For winter cultures, wheat serves well. Both plants are repre- 

 sentative of standard crops for the region under discussion. 



Pathological Effects 



Pathological effects in tops and roots may confirm to a con- 

 siderable extent, the fact that a plant has been poisoned by cop- 

 per. The lengthwise yellow striping of corn and wheat leaves 

 due to toxic amounts of copper is not distinctive since the 

 same appearances may result from various other conditions in- 

 ducing malnutrition, such as those mentioned on a preceding 

 page. Usually, however, careful observation will identify or 

 eliminate these other disturbing factors. 



Root systems grown in coppered soils are also conspicuously 

 injured, being stunted in growth, of harsh and crinkly texture 



