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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 
properties 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, cxygen. ” 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 causes 
the mosaic disease of tobacco, is therefore, 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 peroxidases 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, however, has been done by Woods (1S99, 1902). 
He believes as Sturgis (1S99) does, 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 either the top 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. 
