162 



Scientific Proceedings^ Royal Dublin Society. 

 Table II. 



Ducussion of Results of Tables I and II. 



With regard to the restoration of the original anthocyan pigment (the 

 yellow plastid pigment is never restored), the chief factor seems to be the 

 intensity of colour in tlie untreated leaf. For tlie oxydase which was 

 sufBcient to produce the natural pigment is still there. Yet in some cases 

 the diffusion of inhibitor from adjacent cells on the death of the protoplasm 

 undoubtedly checks the re-formation of colour. The mechanism of this 

 reaction has been fully discussed by Keeble and Armstrong (4), and their 

 explanation is quoted in a former paper by the writer (1). 



In connection with the oxydase distribution, it is apparent that a-naphthol 

 is more susceptible to inhibitors than is benzidine. This is probably because 

 its oxidation products, readily formed, part with oxygen just as readily. The 

 same holds good for guaiacum. Experiments upon the destruction of the 

 oxidation products of these artificial chromogens with Iris germanica leaf- 

 sap bear out this view. Inspection of the table shows that no yellow is 

 present in ISTos. 1, 2, 3, and 5. Of these the first three show well-marked 

 oxydase reactions and natural anthocyan pigments ; whilst the last probably 

 owes its white and pale-blue to the presence of an inhibitor, for here oxydase 

 appears to be absent in the epidermis. No. 4 brings about a marked reaction 

 with both reagents, so its white is due to absence of chromogen, except in a 

 few spots. Accordingly this white is probably a Mendelian recessive. 

 Evidently there is no appreciable amount of inhibitor present, although the 

 yellow patch at the junction of haft and blade is usually productive of such 

 a substance. Examination of Nos. 6, 7, 8, 9 shows that though the natural 

 pigments are well developed, yet the oxydase reactions are not at all 

 pronounced. Each yellow patch is seen to be surrounded by white in the 

 natural state. Thus it appears that cells in the region of those containing 



