154 Scientific Proceedings, Royal Dublin Society, 



Summary. 



1. The presence of oxydase in abundance in the phellogen ring and in 

 sclerenchymatous walls seems to point to tliis enzyme as being concerned in 

 the production of cork and sclerenchyma. 



2. Keeble and Armstrong's bundle peroxydase may extend to the 

 epidermis, and has been detected in the three, four, or five cells immediately 

 abutting on the guard-cells of Cochlearia armoracia. Epidermal oxydase is 

 frequently most active in guard-cells and those immediately in contact with 

 them, as in Wistaria sinensis and Tradescantia virginica. 



3. Plants which yield a brown sap always give the direct oxydase reaction, 

 while those which yield light-coloured saps either give the indirect action or 

 contain tannin or some reducing agent. 



4. The peculiar distribution of oxydase in Iris germanica has been shown 

 to be only apparent, as the presence of a strong reducing agent prevents its 

 detection in certain tissues. It is possible to remove the reducing agent by 

 prolonged dialysis, and the presence of oxydase may then be demonstrated. 

 The reducing substance is not a tannin or a sugar. The mature leaves of 

 Aspidium FiUx-mas also contain a reducing agent which masks the presence 

 of oxydase. After dialysis of the leaf-sap, the indirect guaiacum reaction may 

 be brought about. A more rapid method for separating the reducing substance 

 and enzyme is that employed by Aso for tannin. The precipitation of the 

 enzyme may be effected by pouring the sap into absolute alcohol. The 

 precipitate when redissolved in water gives the indirect guaiacum reaction 

 very intensely. This colour is destroyed by addition of the filtrate. Thus 

 fresh evidence has been obtained in favour of the view that oxydases are 

 universally present in plant tissues, though their immediate detection may be 

 hindered by the presence of reducing agents. 



5. The colours of the periantli leaves of six varieties of Iris have been 

 shown to be due to the presence or absence of a yellow plastid pigment and 

 an anthocyan pigment, which is formed by the action of the epidermal 

 peroxydase on a chromogen. This production of pigment may be inhibited 

 by the presence of the reducing substance of Iris leaf-sap. The latter is distinct 

 from the decolourizing reducing substance of Keeble and Armstrong, as it is 

 active in aqueous solution as opposed to strong alcohol. 



I am indebted to Professor H. H. Dixon for the benefit of his advice and 

 continued interest throughout the work. 



