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



tive root systems in the soil. Not only this, but it may be true 

 that nutrient salts, as well, will be found more actively absorbed 

 by younger and more sensitive root systems than by older ones, 

 or by root systems which for any reason have become quiescent. 

 This would suggest the possibility of choosing to advantage the 

 proper time for applying substances, either to avoid injury or, 

 as in the case of fertilizers, to secure maximum benetit from them. 



Varying Resistance of Individual Cells to Copper 



Not only do old and young roots vary as to toxic effects upon 

 them of copper, but different degrees of resistance between 

 individual cells in the same root and even in the same chain of 

 cells, is clearly shown in the photomicrograph (fig. 13) of a 

 corn root tip which has been exposed to a 1 to 200,000 solution 

 of copper, then colored with K^FeCyg, and sectioned for obser- 

 vation. Tlie dark, abruptly angular line of penetration shown 

 in the section plainly indicates that individual cells may be 

 penetrated by copper while adjacent cells growing under pre- 

 cisely similar physical conditions are not penetrated. If this 

 be not due in some unseen way to morphological peculiarities 

 of root structure, it must be due to individuality in the cells 

 themselves, some of which must be more resistant to penetration 

 by dilute copper solutions than others. 



Summing up the physiological ohservations relating to effects 

 of copper upon plants, we find (1) that individual cells vary 

 (probably) in degree of resistance to penetration by copper 

 salts; (2) that young roots are less resistant than old roots; (3) 

 that roots of certain species of plants (e.g. corn) are less resist- 

 ant than roots of other species; and (4) that toxic effects may 

 be to some extent related to the structure and distribution of 

 root systems. 



DIAGNOSIS OF COPPER INJURY 



In the presence of toxic amounts of copper in the soil, the 

 root systems of culture plants become harsh and crinkly with 

 almost entire loss of root hairs. Consistent with the checking of 

 growing points, root systems are also greatly restricted in extent. 



