tgr1] SCHREINER & SULLIVAN—ROOTS 275 
whole, becomes a cherry red, which varies in depth according to 
the amount of oxidation. 
Reduction by roots has been studied but little. Reduction by 
the tissues of animals and by micro-organisms, on the other hand, 
has been extensively studied (2). The reagents used to indicate 
the reducing power of tissue are chromogens, which on reduction 
by abstraction of oxygen or by the addition of hydrogen yield a 
leuco-base, such as alizarin blue, indophenol blue, lacmus, methy- 
lene blue, indigo carmine, rosanilin, gentian violet; nitrates which 
are reduced to nitrites; sodium selenite and tellurite, which are 
reduced to metallic selenium and tellurium; sulphur, which is con- 
verted to hydrogen sulphide. 
To show reduction we have tried various reagents and. have 
found sodium selenite to be the best medium at our command. 
The selenite used was sodium selenite Merck and commercial 
sodium selenite Merck, the latter for the most part. Solutions of 
©.25 per cent were first used. The solution reacted alkaline to 
litmus and phenolphthalein and was toxic to the seedling. When 
neutralized with hydrochloric acid, however, the toxicity of the 
selenite was greatly lessened. When seedlings were grown in the 
sodium selenite solution made neutral to phenolphthalein and of 
a strength of 0.125 to 0.25 per cent, the parenchyma cells of the 
ends of the root next to the cap were colored pink in a few hours 
by the deposit of selenium. The points of emergence of the 
secondary roots were often colored in the case of the older seedlings. 
After a lapse of several hours the whole root became somewhat 
pinkish. In solution of sodium selenite made #/500 acid by hydro- 
chloric acid, the deposit of selenium at the tip of the root was very 
marked. In alkaline solution the reduction was very little. In 
short, reduction is more marked in slightly acid solutions. Oxida- 
tion, on the other hand, is stronger in slightly alkaline solutions. 
As judged by the quickness with which the deposit of selenium 
is made on the root and the extent and intensity of the deposit, the 
reducing power increases from the time of germination to the sixth 
or eighth day and then decreases. It is still present in seedlings 
thirteen days old, the oldest seedling examined. The oxidative 
Power of the wheat seedling, on the other hand, as judged by the 
