1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 419 



shown by the method of measuring growth of root tips marked 

 with India ink, and noting points at which growth was retarded 

 {B) and arrested {A). 



TABLE XII 



Showing Points at which Boots were Eetarded or Arrested in Growth 



Cultures in Cu, in well water, 



parts per million 03 .05 .08 .1 .3 .5 .8 1. 3. 



Corn E A 



Beans R A 



Squash E A 



Photographs of the three series also indicate an earlier re- 

 tardation of corn root development than of bean or squash root 

 development; and show additionally that the top portions of 

 cultures are not damaged in proportion to the root systems. 



TOXICITY OF COPPER SOLUTIONS TO PLANT ROOTS 



IN WATER CULTURE 



In order to gain some indication of effects in water culture 

 of copper salts upon plants, several series of plants were grown 

 under varying conditions, and effects observed of the kind of 

 copper salts employed, strength of solution used, the kind of 

 plant, and the effects of other salts present. 



Solutions were made in water free from copper, twice dis- 

 tilled; or, where permissible, University of Arizona well water, 

 copper-free. The series were arranged, usually, to carry 0.01, 

 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1.0, 3.0, and 5.0 parts copper 

 per million of water. The cultures were made in 600-c.c. bottles, 

 covered with pasteboard squares saturated with hot paraffin and 

 perforated with three holes for plant seedlings held in place by 

 cotton. 



Effects upon cultures were judged by elongation of roots de- 

 termined by the usual method of marking with India ink 5 mm. 

 back of root tips and noting growth after twenty-four hours. 

 Corn, beans, and squash were the plants employed and the points 



