1 68 The Ohio Naiuratist. [Vol XlII, No. 8, 



based upon soil treatment or reduction of light intensity. Mayer 

 as early as 1SS6, 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. Apjjel and Schlumberger (1911) have considered this 



