580 SPECIAL PLANT PATHOLOGY 



of the mosaic disease of tobacco. The view most generally accepted 

 defines the disease as a disturbance of the enzymatic equilibrium in- 

 duced by unfavorable conditions of growth. An enzymatic disease is 

 physiological in its nature, has its origin within the protoplasmic com- 

 plex, and results in a serious and sometimes permanent impairment of 

 the assimilative functions." Although it has been shown by previous 

 workers that the oxidase and peroxidase content of mosaic leaves is 

 higher than in normal healthy plants, this fact alone does not warrant, 

 Allard thinks, its being considered the initial cause of the disease, for it 

 might well be an effect rather than a cause. It is true that physiologic 

 symptoms attend the mosaic disease such as chlorosis and various mor- 

 phologic changes in the leaves, and hence we have placed it among the 

 physiologic diseases, but notwithstanding, Allard thinks, that parasi- 

 tism accounts for the primary origin of the disease more consistently 

 than the enzymatic hypothesis.^ 



BIBLIOGRAPHY OF NON-PARASITIC DISEASES 



A complete bibliography of non-parasitic diseases up to May, 1915, will be found 

 in Circular 183 Agricultural Experiment Station, University of Illinois by Cyrus W. 

 Lantz, 81-111. 



^Additional papers on mosaic are, as follows: Gilbert, W. W. : Cucumber 

 Mosaic Disease, Phytopath. 6: 143-144 with i plate; Doolittle, S. P.: A new 

 Infectious Mosaic Disease of Cucumber, Phytopath. 6: 145-147; Jaggee, I. C: 

 Experiments with Cucumber Mosaic Disease, Phytopath. 6: 148-151, iqi6. 



