308 Oxydases and Pigments of Plants 



indicates that oxydases have such a general function as is postulated 

 above and that they are part of the respiratory mechanism of the plant. 

 Hence it is reasonable to suppose that the rate of respiration of a 

 given cell is determined by the amount of oxydase present in that cell. 

 If light exercise directly or indirectly a destructive action on the oxydase 

 content of the cell the rate of respiration of the latter will fall off 

 during the day and will rise again after a sufficient exposure to dark- 

 ness has set going the oxydase secreting apparatus of the cell and 

 allowed of the accumulation of peroxydase and organic peroxide. 



It may be that, beside the phenomena of periodicity referred to 

 above, the remarkable respiratory phenomena presented by succulent 

 plants are attributable to their diurnal rhythm of oxydase destruction. 

 During the night the respiration of such succulent plants as Mesemhry- 

 anthemum results in a smaller output of carbon dioxide than that which 

 takes place during the day. Instead of the respiratory substances 

 becoming completely oxidised, they produce incompletely oxidised 

 bodies, namely, organic acids. During the day the normal respiration 

 is resumed and the organic acids which have accumulated at night 

 disappear. 



We propose to investigate this phenomenon in the light of our 

 knowledge of the diurnal variation of oxydase. 



Lastly a brief reference must be made tb the influence of wounding 

 on the liberation of oxydase. As is well known the effect of mutilating 

 a tissue is to produce a speedy and copious liberation of oxydase. The 

 benzidine reagent serves to indicate wound oxydase. That this is so 

 is illustrated in Text-figure 5, which represents white corollas of 



Fig. 5. (From a photograph.) The wound peroxydase of Primula sinejisis. Each of 

 the petals of a dominant white flower of P. sinensis (5 A) was stabbed in three places 

 with a needle. The wounded corolla and also one from an uninjured flower (5 B) 

 were subjected to the action of the benzidine reagent, then washed with water and 

 treated with hydrogen peroxide. The unwounded corolla gave no peroxydase reaction : 

 the mutilated corolla gave an intense reaction in the neighbourhood of each wound 

 (see text). 



