326 Scientific Proceedings^ Royal Dublin Society. 



varied as well as the wave-length. As far as the experiments went, however, 

 there was no marked difFerence in the behaviour of the flowers under the two 

 jars. In both diminution of liglit caused the peroxidase reactions to become 

 more intense. 



Summary. 



1. The peroxidase reactions of related species and varieties of Iris are 

 similar, though the distribution and quantity of anthoeyanin may be very 

 different. 



2. The Pogoniris group is characterized by an absence of active 

 peroxidase ; in the Apogon the distribution is variable ; while in the Xiphion 

 group the reactions are as a rule well marked, especially in /. Xiphium. 



3. In Xiphium there is a definite inhibition area on the claw of each of 

 the falls. 



4. Where peroxidase tests have a negative result when the reagents are 

 applied in the usual way, it is possible to demonstrate the presence of the 

 enzyme by treatment with hydrogen cyanide as advocated b}' Keeble and 

 Armstrong, or by toluene water. 



5. By the above treatment an inhibitor is removed. This is probably 

 not a chemical reaction, but since the reagents render protoplasm permeable, 

 it is apparently to be accounted for by the diffusion of the inhibitor. 



6. When Iris flowers are kept in darkness, the quantity of active 

 peroxidase increases, and in' one case the production of organic peroxide was 

 recorded. Some varieties, however, show very little increase in the enzyme 

 activity. 



7. This alteration in peroxidase activity is not sufficiently rapid to 

 seriously vitiate the results obtained with various species of Iris flowers 

 picked after exposure to unequal periods and intensities of illumination in 

 the garden. 



8. Owing, possibly, to complications introduced by inhibitors, it is 

 impossible in Iris to correlate the distribution of peroxidase and antho- 

 eyanin, the latter frequently appearing in the absence of the former in an 

 active state. 



I take this opportunity to acknowledge my indebtedness to Mr. W. 

 R. Dykes for his kindness in identifying the flowers, and for valuable 

 suggestions ami criticism. 



