1909] SCH REINER & REED— OXIDIZING POWER OF ROOTS 361 





growing cells in the region of greatest elongation is not intensively 

 colored; the more slowly growing portions of the root possess the 

 purplish color, but it becomes less intense as one passes to the upper 

 parts of the root. 



The superior oxidizing power of the meristematic tissues of the 

 plant is not only shown by the narrow zone of deep color formed 

 on the primary meristem of the apical portion of the roots, but also 

 by the small dots of color produced on that portion of the root from 

 which secondary roots arise. If a wheat root 8 to io cm in length 



placed in a solution of naphthylamine it will exhibit, in addition 

 to the deeper colored zones near the apex, dark- purple spots at the 

 places where secondary roots are forming and are about to break 

 through the cortical layers of the primary root. If secondary roots 

 are already present they show the same zones of colors already 

 Ascribed for the primary roots. 



The concentrations of naphthylamine used in solution cultures 

 are necessarily low on account of its slight solubility in water, but 

 ire sufficiently strong to show the oxidation. In ordinary practice 

 10 Parts of naphthylamine to a million (io ffl * per liter of water) 

 is a suitable concentration to use. This concentration will eventually 

 retard the growth of wheat plants, but is not detrimental to growth 

 ^ the length of time usually required to demonstrate the oxidizing 

 P°wers of the plant roots. A concentration of 5 parts per million 

 sometimes acts as a stimulant to growth. 



Benzidine is another chromogen, which is oxidized by plants 



1 may advantageously be used to demonstrate their oxidizing 

 acti on. It is onlv slightly soluble in water, but in weak, colorless 

 ol ution it is readily oxidized by plant roots to an insoluble dye which 

 ^'es the roots a blue-black or black appearance. Benzidine is 

 !l 8 h tly toxic to plant growth, but does not cause pathological con- 

 dlti °ns within the time reouired for demonstrating the oxidizing 

 P°*er of the plant roots. A concentration of 5 parte benzidine to 

 a nUUon of water will give good results and does not in J ur ^\ hea 

 ro °ts in 24 hours, although that concentration may eventually inhibit 

 growth. 



L T he effect of oxidation may easily be demonstrated by allowing 

 the roots of wheat plants to grow in a 5 parts per million solution ot 



and 



