294 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



oxidases interfered with the action of diastases in the 

 plant. With this view as to the cause of the injurious 

 symptoms, Pozzi-Escot (1905) expressed agreement, and 

 Doby (1912), in the course of an investigation on the potato 

 leaf-roll disease, found that oxidases, both of the laccase 

 and tyrosinase classes, were present in abnormal quan- 

 tities in the diseased tissues. 



Allard (1915) has, however, shown that it is possible to 

 induce the disease in healthy plants by inoculating them 

 with the sap pressed from those which are affected. 

 Furthermore, dilution of the sap up to 1 part in 10,000 of 

 water did not entirely stop transmission of the disease. 

 Thus it appears certain that the excess of oxidases is a 

 pathological symptom of the mosaic disease of tobacco 

 and by analogy of the mulberry leaf disease rather than 

 a primary cause. An organism causing the infection has 

 not been discovered as yet. 



THE " CURLY-TOP " DISEASE OF THE SUGAR 

 BEET. 



Recently Bunzel also (1913) has investigated the oxidase 

 content of normal leaves of the sugar beet, and of those 

 affected with the " curly-top " disease. This had been 

 studied by Townsend (1908) and by Shaw (1910), and has 

 been described by the latter as resulting in "an inward 

 curling of the leaves, a distortion of the veins of the affected 

 leaves, hairy roots, and checked growth." Heavy losses 

 are occasioned by it both by reason of the stunting of the 

 growth and of the -prevention of seed production. Its 

 cause was and has remained quite unknown, though it 

 was shown by Ball (1911) that it develops after the bite of 

 an insect, the curly-top leaf hopper (Eutettix tenella). 



Bunzel's careful investigation into its symptoms, as 

 revealed by a very elaborate series of measurements upon 



