1 52 Scientific Proceedings, Royal Dublin Society. 



the purple estr.aot, probably by oxidation, it must be remembered that this 

 reagent can have a reducing action in the presence of an easily reducible 

 substance, such, for instance, as silver hydroxide. Assuming it to be an 

 oxidation, it was thought that the reducing action of the leaf-sap might 

 restore the original purple, but this was not found to happen. 



Precipitation of the enzymes by pouring the leaf-sap of Iris into strong 

 alcohol also serves to separate the reducing substance whicli is found in the 

 filtrate. The precipitate now gives the indirect guaiacum reaction, the colour 

 being destroyed by addition of the filtrate. 



Beducwg agents in other plants. 



In the preliminary experiments it was noticed that whereas very young 

 leaves of Pteris aquilina gave the indirect guaiacum reaction, the mature 

 leaves gave no reaction for oxydase or for tannin. Pohjpodium aureuni 

 leaves gave the indirect reaction, wliile As2}idwm Filix-mas gave none, 

 and even behaved like Iris leaf-sap, but not to such a marked extent. The 

 pressed leaves afforded a light-green sap ; this when dialyzed for several days 

 gave the indirect guaiacum reaction, but further dialysis failed to bring about 

 a direct reaction. It must be distinctly understood that these reducing agents 

 are active in aqueous solution, and so are different from the reducing agents 

 of Keeble, Armstrong, and Jones (16) to which the decolourization of flower 

 anthocyan pigments is due, for these only become active as dehydration 

 proceeds. 



Tlie pigments of the flower of Iris. 



The flowers of Iris are roughly divided into two classes, the purple 

 and the yellow. Of these the yellow owe their colour to a plastid pigment, 

 while the purple is due to an anthocyan pigment dissolved in the cell 

 vacuoles. 



Six varieties will be considered here : — 



1. Purple perianth leaves, with yellow hairs, and white streaked with 



brown markings at base, the latter being due to tlie presence of 

 yellow plastids and purple sap in the same cells ; the purple is very 

 noticeable in the epidermal papillae. This is Iris germanica. 



2. Same as 1, but the purple is paler all over. Iris pallida. 



3. Same as 1, but the purple is very intense, and contrasts sharply with 



large white patches, about equal in area to the purple region. Iris 

 pallida, var. victorine. 



4. Deep yellow, witli red-brown markings at base. Iris sp. ? Canadian. 



