on Green Leaves and other Parts of Plants. 177 
previously to precipitation. In the case of the Vicia Faba 
rootlets we found the reaction to take place exactly as de- 
scribed by Pfefifer. 
Wurster 1 recommends the use of tetramethylparaphenylene- 
diamine, which acquires a violet colour on exposure to active 
oxygen, whereas it remains entirely unchanged on exposure 
to ordinary passive oxygen. It is best used in the form of 
test-paper, in which form it indicates the presence of active 
oxygen in various substances and mixtures, more especially 
plant-juices. It does not, however, show what particular form 
of active oxygen is present, and it also becomes coloured by 
nitrites. 
As regards plant -juices, Pfefifer objects to Wurster’s experi- 
ments as being made with the contents of dead, not of living, 
cells. Whether the same objection would apply to one of 
Wurster’s experiments, in which he operates on Leontodon 
leaves crushed under mercury, maybe questioned. Bokorny 2 
objects to Wurster’s test because it shows a reaction with so 
many substances, including ordinary oxygen, and under so 
many circumstances that it cannot be considered as indicating 
the presence of active oxygen at all, adding that for hydrogen 
peroxide starch iodide solution is a far more sensitive test. 
To this Wurster replies 3 , re-asserting the superiority of his 
test over any other, and again stating that it is not in the 
least affected by ordinary oxygen, however long applied. Re- 
ferring to Pfefifer’s experiments he says that the plants, or 
rather parts of plants, with which the latter worked do not 
affect his own test-paper. 
Without pronouncing any opinion on the divergent views of 
various observers, we may state that we have tried several 
tests for the presence of active oxygen in the expressed juices 
of plants, more especially starch iodide solution and Wurster’s 
test, the latter in the form of test-paper, called by us, following 
the example of the inventor, simply ‘ tetra-paper.’ We find, 
as Wurster did, that the expressed juices of various plants 
1 Ber. d. d. Chem. Ges. 19, 3195. 
3 lb. 21, 1525. 
2 lb. 21,1 101. 
