230 SOME RECENT RESEAECHES IN PLANT PHYSIOLOGY 



role can be assigned to them. This point will be discussed 

 later on. 



Again, it is well known that certain tannins act as 

 inhibitors of oxidase action. Thus it was found by the 

 author that sap from the young red leaves of Vitis Veitchii 

 shows the direct reaction with guaiacum, whereas sap of 

 the more mature green leaves, which contain tannin, give 

 no reaction. Furthermore, Aso (1890) succeeded in 

 separating oxidases from tannin by precipitating them 

 with alcohol. It is also possible that the failure of extracts 

 of the Fucacese to show oxidase reactions may be con- 

 nected with the presence in them of fucosan, which has 

 recently been shown by Kylin (1913) to be a tannin-like 

 substance. These extracts are efficient reducing agents, 

 as they almost decolorize dilute methylene blue and the 

 guaiacum blue produced by leaf sap of Hedera. All the 

 author's attempts to obtain an active oxidase from these 

 algae by dialysis or precipitation were quite unsuccessful. 



MODE or ACTION OF INHIBITORS. 



Enough has been said to demonstrate the presence of 

 reducing agents which act as inhibitors. All reducing 

 agents are, of course, bodies which are themselves very 

 prone to oxidation. In fact, it is possible to arrange such 

 unstable substances in a scale, in which each would yield 

 oxygen to the one above it and take it from the one below 

 it. By this transmission of oxygen from one compound 

 to another considerable changes may take place in a cell 

 without any absorption of gaseous oxygen, as Bunzel 

 (1912) has pointed out. Whether naturally occurring in- 

 hibitors actually do lessen oxidase activity has not yet 

 been completely investigated. Measurements with Bun- 

 zel's apparatus would seem the most likely way in which 

 to obtain decisive evidence. At present there appears to 



