346 BROOKLYN BOTANIC GARDEN MEMOIRS 



We may therefore conclude that the substances necessary for 

 oxidation do not suddenly migrate into the nucleus at the moment 

 of injury, but that they must exist there before the cell is injured. 



We may ask why the nucleus does not become darkened in the 

 normal condition of the cell. The investigations of several workers 

 have made it probable that the pigments produced by oxidation under 

 normal conditions are at once reduced, giving up their oxygen to other 

 substances in the cell. When injury occurs the reduction is checked 

 more rapidly than the oxidation, with the result that the pigment 

 accumulates. 



It is also possible that injury causes the admission of oxygen to 

 the cells. 



In order to test the effect of the indophenol reaction on leaves of 

 Monotropa they were torn in two and placed in a mixture of equal 

 parts of aqueous i percent paraphenylene diamine and saturated 

 aqueous alpha naphthol. It was found that the result depends some- 

 what on the condition of the reagent. In the most favorable cases 

 the cells which were torn open became pale purple in color almost 

 at once, showing that the reagent readily penetrated them. Usually 

 the cell contents (cytoplasm, nucleus and vacuole) became at first 

 uniformly tinged with purple. After a while the nuclei would usually 

 assume a deeper purple than the remainder of the cell contents. 



The cells lying a little further from the torn surface, which were 

 injured but not actually torn open, showed at first a pale yellowish 

 color which in some cases became deeper with time and in other 

 cases gave way to a purplish tint. In most of these cells the nuclei 

 gradually became deeper in color than the other cell contents. Later 

 the cytoplasm became in some cases so deep in color as to obscure the 

 nuclei. Cells lying still further from the torn surface changed very 

 slowly (many remaining unchanged after some hours) so that it was 

 evident that the reagent penetrated from the torn surface and not 

 through the outer cell walls (which are normally in contact with the 

 air.'" 



In most cases the general result, after a few minutes, was a deep 

 purple band along the torn edge: inside the purple band was a yellow- 

 ish one of irregular outline, followed by nearly colorless intact cells 

 further away from the torn edge. 



In I percent aqueous paraphenylene diamine the results were 

 similar but the purple color was replaced by a dirty brownish-red 

 (with more or less purplish tinge). 



It should be pointed out that these results are most striking with 



" More rapid penetration from cut or torn surfaces is commonly observed in 

 the entrance of reagents into leaves, petals, etc. 



