SOME RECENT WORK ON PLANT OXIDASES 123 



In many flowers there is an inhibitor in cells which contain 

 plastid pigments, and in all cells between them and the upper 

 surface. This was observed in Primulas by Keeble and Arm- 

 strong, and by the author in varieties of Spanish Iris. The 

 contrast of the dark colour of the benzidine oxidation products 

 in the petals with the colourless inhibition areas is frequently 

 very striking. 



The white flowers previously mentioned as containing in- 

 hibitors have been shown to be Mendelian dominants, when 

 crossed with coloured varieties, whereas the whites which are 

 white through lack of chromogen behave as recessives. 



The Role of the Oxidases in Plant Pathology 



Since upon the death of the protoplasm oxidases act without 

 the restraints to which they are subject during its life, it might 

 well be supposed that conditions unfavourable to the normal 

 metabolism of the cell might result in increased oxidase activity. 

 This has been found true in a number of instances. It had been 

 observed that when mulberry trees were cut back too frequently 

 an abnormal yellow colour and crinkled appearance resulted in 

 the leaves. Suzuki 1 investigating this found that an excessive 

 production of oxidases had taken place in such yellow areas. 

 He attributed this to the lack of proper nutrition of rapidly 

 growing tissues. Much the same phenomena were observed by 

 Woods 2 in the "mosaic disease" of tobacco plants which have 

 been cut back. He also demonstrated that the condition was 

 rendered more acute by the application of certain manures 

 which increase the rate of growth. 



More recently Bunzel 3 has investigated the oxidase content 

 of normal leaves of the sugar beet, and of those affected with 

 the "curly-top" disease, which has been shown by Ball 4 to 

 develop after the bite of an insect, the curly-top leaf-hopper 

 {Eutettix tenella). Bunzel ascertained that the leaves of the 

 curly-top plants had an oxidase content two to three times 

 as great as the healthy and normally developed ones. No 

 marked differences, however, could be detected between the 

 roots of the two kinds of plants. Bunzel admits that this 



1 Suzuki, Bull. Agric. Coll. Tokyo, 1900, 4, 167 and 267. 



* Woods, Bull. 18, Bur. Plant Industry, U.S. Dept. of Agric. 1902. 



s Bunzel, Bull. 277, Bur. Plant Industry, U.S. Dept. of Agric. 1913. 



4 Ball, Bull. 66, Bur. of Entomology, U.S. Dept. of Agric. 1911, pt. 4, p. 33. 



