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VII. 



OXYDASES AND THEIE INHIBITORS IN PLANT TISSUES. 

 By W. E. G. ATKINS, Sc. B., A.I.C., 



Assistant to the Professor of Botany, Trinity College, Dublin. 



[Read June 24. Published Augd6T 20, 1913.] 



In the course of some work with Professor H. H. Dixon (9) on osmotic 

 pressures in plants, the brown colour of tlie sap as expressed from many 

 tissues was very noticeable. We subsequently found that this effect was well 

 known to be due to the action of oxydases, as had been shown by Wheldale (28), 

 Kastle (14), and others. In some cases, however, the sap was light in colour, 

 and no oxydases could be detected. It lias been pointed out by Aso (2) that 

 tannin hinders the action of oxydase on the usual reagents employed for the 

 detection of the enzyme, and Hunger (12) states that sugars behave in a 

 similar way. We were able to account for a number of cases of undarkened 

 sap by proving the presence of tannin. Some, however, remained over, and 

 in view of tlie great importance now attaching to the action of respiratory 

 enzymes, owing to the work of Palladiu and his collaborators (18, 19, 20), to 

 their production of organic acids, as shown by Weevers (27), to their role in 

 plant pathology, as worked out by Bunzel (5, 6, 7), Woods (29), Shaw (25), 

 and Suzuki (26), in the study of technology, as pointed out by Bailey (3), in 

 the ripening of fruits and seeds, owing to the work of Applemau (1), 

 Eckerson (11), and others, and in the study of genetics, by Keeble and 

 Armstrong (15, 16, 17), it seemed advisable to make an attempt to explain 

 why the oxydase could not be detected in certain saps. 



The possibility of the presence of reducing agents at once presents itself, 

 as such liave been found by many workers, notably by Ozapek (8), and by 

 Schreiner and Sullivan in roots (23, 24). 



Distrihution of Oxydases in Certain Tissues. 



The direct guaiaeum oxydase reaction was given by the sap of the 

 following leaves : — Hedera Helix, Syringa vulgaris, Magnolia acuminata, 

 Catalpa bignonioides, Fraxiniis oxyphylla, F. excelsior, HeUanthiis miiltiflorus ; 



