452 University of California Publications in Agricultural Sciences [Vol. 1 



(2) Young and old wheat and corn roots were placed in 10 

 p. p.m. Cu in distilled water and 10 p. p.m. Cii in nutrient solution, 

 with the following results : 



10 p.p.m. Cu, distilled water — 20 hours 

 10 days old: Young wheat; flaccid?; strong biuret t«st; strong KiFeCje test 

 60 days old : Old wheat ; not flaccid ; faint biuret test ; distinct KiFeCys test 

 10 days old: Young corn; flaccid; strong biuret test; strong K^FeCye test 

 60 days old: Old corn; flaccid; distinct biuret test; strong KiFeCyr, test 



10 p.p.m. Cu, neutralized nutrient solution — 20 hours 

 10 days old : Young wheat ; not flaccid ; doubtful biuret test ; faint KjFeCyp 



test 

 60 days old: Old wheat; not flaccid; none or doubtful biuret test; faint 



K^FeCve test 

 10 days old: Young corn; not flaccid; faint biuret test; distinct K4FeCy6 



test 

 60 days old : Old corn ; not flaccid ; distinct biuret test ; distinct K4FeCye 



test 



This shows very distinctly the ])revention of toxic action upon 

 plant roots through the protective action of other solids in solu- 

 tion, as already observed in water cultures by measurements of 

 root growth. It is noteworthy in this connection that corn roots 

 generally seem to be more sensitive to the action of copper salts 

 than the roots of wheat or peas. 



In order to examine still further into the relative resistance ■ 

 of old and young root systems to copper salts, a solution of 5 

 p.p.m. Cu in di.stilled water was used, the time being varied 

 from twenty to two hundred hour.s. The results of these obser- 

 vations indicate that, witli wlieat and corn roots, the penetration 

 of copper is distinctly more rapid in young than in old material. 

 Peas did not give clear results. 



It appears from these observations, first, that the accumula- 

 tion of copper in plant roots is distinctly due to tbe migration 

 of dissociated ions into the root .systems, where they are fixed b>- 

 protoplasm, in which combination they are identified by means 

 of the biuret test. Second, the presence of nutrient salts very 

 distinctly les.sens the effect of a 10 p.p.m. copper .solution upon 

 sensitive young growing plant roots. Third, old quiescent plant 

 roots developed in a nutrient solution are distinctly less sensitive 

 to copper salts than young roots which are still actively growing. 



