Atkins — Oxidases and their Inhibitors in Plant Tissues. 325 



Discussion of Results of Table VI. 



It is atouce evident that the absence of light permits of the accamulation 

 of peroxidase in an active condition, and even leads to the formation of 

 organic peroxide in the veins of /. Monnieri. The effect apparently is only- 

 brought about slowly, for although it is noticeable after twenty-one hours, it 

 only becomes well marked after sixty-six. It may also be seen tliat the age 

 of the Hower is without influence on the intensity of the reactions, except tliat 

 in the buds the latter are not so strong as in the more mature flowers. Since 

 these buds opened in the dark, and were tightly folded when placed there, it 

 is clear that the absence of active peroxidase cannot be due to its destruction 

 by light. 



In /. xipliioides, like No. 66, whicli was of a dark claret-colour, with spots 

 of deeper liue, even sixty-six hours in darkness failed to bring about the pro- 

 duction of peroxidase, except in the veins of the claw. Similar flowers which 

 had been in the dark press for ninety-three and a hundred and fifteen liours 

 behaved in the same manner. The almost complete absence of peroxidase 

 activity from flowers of such a deep colour is hard to reconcile with the view 

 that the pigment is produced as the result of the action of the enzyme. Since 

 there remains the possibility that tlie anomaly may be due to the presence of 

 an inhibitor, which is set free by tlie death of the cells, so that it can diffuse 

 into places from which previously it was absent, it was decided to test the 

 point further. . 



Falls of both I. Monnieri and of the claret-coloured variety of /. 

 xiphioides were treated for twenty-four hours with 0"2 per cent, hydrogen 

 cyanide, and with water saturated with toluene. Tlie cyanide was then 

 removed by allowing the tissues to steep in toluene water for another twenty- 

 four hours, after which they were well rinsed. Both varieties were found to 

 show a + + reaction in tlie veins, and in this respect treatment with toluene 

 alone was as effective as with cyanide. Thus an inhibitor was removed, 

 or more probably permitted to diffuse away. This, however, furnishes no 

 proof that the inhibitor was not free to act in the cells before the treat- 

 ment. 



An attempt was made to ascertain whether yellow or blue light was the 

 more injurious to peroxidase production, by placing similar flowers inside 

 double-walled bell-jars filled with potassium bichromate and ammonia copper 

 sulphate, as usually employed in laboratories as light-screens. It was 

 abandoned, since it was recognized tliat such screens are in no sense capable 

 of affording accurate results, for the total quantity of incident light is also 



SCIENT. PROC, R.D.S., VOL. XIV., NO. XXIV. 3 F 



