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XXIV. 



OXIDASES AND THEIR INHIBITOES IN PLANT TISSUES. 



Part IV.-THE FLOWERS OF IRIS. 



By W. R. G. ATKINS. Sc.U., F.I.C., 

 Assistant to the Professor of Botany, Trinity College, Dublin. 



[communicated by professor H. H. DlXON, F.R.S.] 

 [Eead Novemeeii 24, 1914. Published January 5, 1915.] 



In Part II of this work an account was given of the peroxidase reactions of 

 about thirty Iris flowers of various species. In the present paper the list has 

 been considerably extended, and much of the previous work has been repeated; 

 with a view to finding out how far tlie activities of oxidising enzymes are 

 dependent upon the age of the flower, and otlier factors such as illumination. 



Undoubtedly unopened buds of forms having an anthocyan pigment are 

 of a deeper colour than the mature flowers. This is due partly to the rapid 

 enlargement of the cells, with consequent dilution of the pigment, and partly 

 to the fading of the colour in sunliglit. The results obtained here go to show 

 that the peroxidase reactions in buds and mature flowers differ ueitlier in 

 distribution nor in intensity. Withered flowers, however, give erratic results, 

 as might be expected. 



The reagents were applied as described in the previous papers, but Merck's 

 perliydrol, suitably diluted, was employed instead of ordinary commercial 

 hydrogen peroxide, which is slightly acid and requires to be neutralized. In 

 every ease the falls, standards, styles, and stamens were tested, but the reac- 

 tions recorded are those of the falls and standards unless tlie contrary is 

 stated. It was observed that the stigmatie surface and central vein of the 

 style gave well-marked reactions in almost every case, and in none was tliere 

 a complete absence of peroxidase activity. The pollen sacs, too, contained 

 active peroxidase. These Iris reactions are all of the indirect or peroxidase 

 type. 



Some flowers, such as those of the large "Canadian" variety of 1. pseiidacorus, 

 show intense actions throughout. Accordingly, it was suspected that the foliage 

 leaves of this species might be free from the reducing inhibitor met with in 

 those of /. germanica. Such a supposition was found to be incorrect, for the 



SOIBNT. PROO. E.D.S., VOL. XIV, NO. XXIV. 3 E 



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