THE OXLDASES IN RELATION TO PLANT PATHOLOGY 295 



the oxidases present in the various organs both of healthy 

 and diseased plants, has brought to light the remarkable 

 fact that oxidases are present in the leaves of the latter 

 in from two to three times as great quantities as they are 

 in the former. The measurements were carried out upon 

 the sap pressed from the tissues through a piece of raw 

 silk. They are therefore open to error owing to the fact 

 that the protoplasm of the cells acts as a semi-permeable 

 membrane during pressing, as shown by Dixon and Atkins 

 (1913, 1). The errors thus introduced are, however, well 

 within the range of the large variations found by Bunzel, 

 and could be completely avoided by previous freezing of 

 the tissues in liquid air. 



The oxidase determinations were carried out with the 

 apparatus previously described (see p. 243), and the 

 results are expressed in terms of the unit adopted in 

 testing the method viz., an oxidase solution of suqh a 

 strength that 1 litre of it could effect the oxidation of 

 the equivalent of 1 gramme of hydrogen. 



Bunzel first of all investigated the oxidase content of 

 normal organs, and the variations in it produced by altera- 

 tions in external conditions, such as the illumination. 

 Some of his results are quoted in the following babies. The 

 experiments were carried out during the month of August. 



TABLE LXVI. 



JUICE PRESSED FROM HEALTHY BEET PLANTS. 



Oxidase Units. 



Small mature leaves, up to 15 cm. . . . . 0-499 

 Large mature leaves, 30 to 40 cm.^ . . . . 0-184 

 Very young leaves, 2 to 7 cm. . . * . . . . 0-180 



From this it may be seen that those leaves which are 

 apparently normal, but fail to develop to full size, contain 

 nearly three times as much oxidase as either large mature 

 leaves or very young leaves. 



