Physiological Observations 201 



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

 p.p.m. Cn in distilled water and 10 p.p.m. Cu in nutrient solution. 

 with the following results : 



10 J).]). 111. Cu, distilled water — 20 hours 

 10 days old: Young wheat; flaccid?; strong biuret test; strong KiFeCyo test 

 60 days old: Old wheat; not flaccid; faint biuret test; distinct K^FeCy^ test 

 10 days old: Young corn; flaccid; strong biuret test; strong KiFeCyo test 

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



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

 10 days old: Young wheat; not flaccid; doubtful biuret test; faint K,FeCy6 



test 

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



K^FeCy^ test 

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



test 

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



test 



This shows very distinctly the prevention 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 w^heat 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 distilled water was used, the time being varied 

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

 vations indicate that, with wheat 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 the migration 

 of dissociated ions into the root systems, where they are fixed by 

 protoplasm, in which combination they are identified by means 

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

 distinctly lessens 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. 



