i68 
The Ohio Naturalist.. 
[Vol. XIII, No. 8, 
based upon soil treatment or reduction of light intensity. Mayer 
as early as 1886, showed that renewing soil in the hot-bed gave 
wonderful results in reducing the disease. By proper liming and 
shading, Sturgis (1899, 1900), showed that tobacco could be 
grown practically free from mosaic disease, on soils where calico 
had been prevalent. Koning (1899) regarded the use of lime and 
mineral fertilizers as valuable aids to the production of a healthy 
crop. Loew (1900, p. 25) says, “Some planters entertain the 
belief that a too extensive use of mineral fertilizers favors the 
disease and indeed, those fields had the least number of diseased 
plants which had received chiefly organic manure. ” The use of 
new soils for seed-beds and a seed treatment with copper sulphate, 
is proposed by Gontiere (1900). Eliminating root injury in all 
ways; preventing too rapid a growth due to using an excess of 
nitrogenous fertilizer and avoiding improperly drained soils, are 
Woods’ (1902) ideas for combatting the disease. Hunger (1903, 
1904, 1905) believes that diseased plants and roots tide the disease 
over from year to year, and recommends that they should be 
removed from the fields. He regards the avoidance of all injuries 
to plants important. Bouygeres and Perreau (1905) advise the 
elimination of manures. Hinson and Jenkins (1910, p. 10) say, 
“So far the only known methods of lessening “calico” in the seed¬ 
bed, are avoiding the use of tobacco water, as noted before, and 
the probable good resulting from steam sterilization.” Different 
light intensities and the use of colored lights are possible factors 
influencing this disease, according to Lodweijks (1911). 
The prevention of tomato mosaic under glass is discussed by 
Westerdijk (1910). She states (pp. 6-7), “The grower can reduce 
this disease by white-washing the greenhouse as soon as the first 
signs of yellow spots are noticed. ” As mentioned before, the 
writer has observed that over forcing is liable to cause its ap¬ 
pearance in the greenhouse. 
Other Plant Diseases Apparently of an Enzymic Nature. 
Besides the work of Woods (1899, 1902), Heintzel (1900) and 
Hunger (1903) on tobacco mosaic and Suzuki (1902) on the Mul¬ 
berry disease, mentioned above, there are several more recent 
investigations which take up certain pathological problems from 
the standpoint of the enzymic disturbances involved. Pozzi- 
Escot (1905) assigns various maladies to an over abundance of 
oxidases. It is believed that a counter action takes place between 
these and beneficial enzymes which are active in metabolism. 
Sorauer (1908), in making a study of the leaf curl of potatoes, 
found that no specific organism was connected with this trouble, 
but an enzymic disturbance did present itself. In comparing the 
diseased and healthy tubers, he found great differences in enzymic 
reactions. Appel and Schlumberger (1911) have considered this 
