1 64 The Ohio Naturalist. [Vol. XIII, No. 8. 



succumbing from the effects of certain outward, injurious in- 

 fluences. In a later paper (1905), he states that mosaic diesase 

 is simply due to a disturbance in the metabolism of the host. 

 Meterological conditions, during the growing season, at least 

 in the case of tobacco, are influential agents and the physical 

 ]jroperties of the soil are more important than the chemical. 

 He regards the normal tobacco plant as having mosaic disease 

 in a latent state, or at the least being predisposed towards it, 

 its appearance depending upon external conditions. Westerdijk 

 (1910) says, that mosaic disease is worse in the tropics where 

 light intensity is stronger. She shows that shading tomato 

 plants in the greenhouse has a marked effect in controlling this 

 malady. Heintzel (1900) also believes that this trouble can be 

 explained from the physiological standpoint, but he restricts 

 the cause to abnormal conditions resulting in a localized over- 

 production of oxidizing enzymes. He states (p. 42), "From 

 various observations I believe, that this disease producing sub- 

 stance in the tobacco plant is an enzyme, or apparently enzymic 

 in nature, which forms or is produced from or by the plant itself 

 under certain conditions." He describes this enzyme by saying 

 that "it is precipitated by alcohol; is soluble in water; loses its 

 properties on boiling; but lowering the temperature even to 

 freezing has no effect upon it; it does not increase outside of the 

 host; salicylic acid interferes with its active properties; it retains 

 its active properties in the dry state as well as in solution; it is 

 diffusible, disturbs cellulose and chlorophyll; at the same time 

 it forms a gas, oxygen. " All these properties so closely relate 

 it to an enzyme, that one can call it an enzyme without a doubt. " 

 He closes his paper by saying (p. 45), "The enzyme which catises 

 the mosaic disease of tobacco, is thei^efore, known as an oxidase. " 

 Koning (1900) mentions, that he observed a peculiar dark rose 

 color on media, whenever he placed pieces of diseased tissue on 

 agar plates; this being more noticeable than in cases where healthy 

 pieces were used. It appeared to him as though an oxidizing 

 body existed. This seems to harmonize with Woods' (1S99, p. 

 751), results, showing that ])croxidases at least, are diffusible. 

 He found that peroxidases would diffuse into agar, if small pieces 

 of Hibiscus wood were placed upon such media. 



The most detailed and convincing work in support of the 

 enzymic theory, howe^^er, has been done by Woods (lcS99, 1902). 

 He beHevcs as Sturgis (1S99) docs, that soil conditions are impor- 

 tant factors to be considered, (1902, p. 23). "Close clayey soils, 

 packing hard after rains and requiring constant tillage are not 

 favorable to even growth of cither the to]) or the roots of tobacco 

 plants." In the south poorly drained soils are said to favor 

 the development of the disease. He is not of the opinion that 

 a lack of soil nutrients has anything to do with its appearance. 



