THE OXIDASES IN RELATION TO PIGMENTATION 263 



limiting factor, whereas in Nos. 5 to 9 the presence of an 

 inhibitor is indicated, and this is borne out by the results 

 obtained after treatment with hydrogen cyanide. 



Very striking are the colours developed on applying the 

 reagents to the Spanish Iris /. xiphium. The group is 

 characterized by the intensity of its peroxidase actions, as 

 may be seen from Table LX. There is, however, a very 

 definite inhibition area, which remains quite uncoloured. 

 This coincides with the distribution of the deep yellow 

 plastid pigment on the haft of the falls. Prolonged treat- 

 ment with the reagents in part obliterated this white area, 

 apparently because the inhibitor slowly diffused away. All 

 this is quite similar to the behaviour of 'Primulas, as shown 

 by Keeble and Armstrong. 



TABLE LX. 

 XIPHION GROUP. 



In the Pogoniris group, however, one is faced by a most 

 puzzling series of reactions, as shown in Table LXI. With 

 remarkable unifgrmity, the peroxidase reactions of this 



