1 6d The Ohio Naturalist. [Vol. XIII, No. 8, 



so than the "yellow-green mosaic" which is scarcely known to 

 many tobacco growers. Sturgis (1899, p. 258) states, ''It is 

 evident that in this so-called "spotted disease" of tobacco, we 

 have a disease very similar to, if not identical with, that known 

 in Connecticut as "spotting" and furthemiore, that this disease 

 is as distinct from mosaic of foreign tobacco as "spotting" is 

 from "calico." If the statements of the Russian investigators 

 above mentioned are correct (and there is ever}^ reason for so 

 regarding them), "spotting" is probably due to excessive trans- 

 piration induced by sudden atmospheric changes." In regard 

 to "spotting," in this country, he says (1899, p. 254, "It is a 

 peculiar disease, not very common, not confined to any one locality 

 and not characteristic of any special soil. As I have seen it — 

 it is signalized by the presence on the leaf of small circular spots. 

 These usually occur in the greatest numbers at or near the tips of 

 the leaves, at first — yellow in color — irregular in outline — . The 

 tissue within the border finally dies and becomes almost white, 

 but except in severe cases, it does not break away from the leaf. " 

 He goes on to say that microscopic examinations have never 

 sho^^^tl the presence of fungi or bacteria. "Nothing further, 

 therefore, can be said regarding this trouble, nor would it have 

 been considered worthy of mention were it not for its resemblance 

 to a disease of tobacco which occurs in Europe and Asia. " Woods 

 (1902) does not seem to mention this trouble. 



There is no serious confusion in this country regarding 

 these troubles; they seem to be distinguishable. According to 

 Sturgis (1900), the "spotting" which may occur at times is not 

 undesirable to a limited extent, as it enhances the value of to- 

 bacco. It is sometimes artificially produced by spraying with 

 certain chemicals. 



Causes of Mosaic Disease. 



The causes which have been assigned to this disease are 

 numerous and varied. A great many have been recklessly 

 assigned, as often is the case when some undetermined disease 

 has long resisted the efforts of investigators. According to Hunger 

 (1905) it is still believed by many growers in Europe that "bad 

 intentions" on the part of some one had much to do with its 

 appearance. In Deli it was claimed that the disease appeared 

 where the Coolies had urinated on the plants in the hot-bed, 

 while in other cases laborers were accused of j^ossessing the 

 "warm hand." 



Among recent students the cause of mosaic disease is generally 

 considered to be due either (1) To bacterial infection, (2) The 

 Viras theory, (3) A physiological disturbance. 



1. The Bacterial Theory. — Here a specific organism, a bac- 

 terium, is stated to be the cause of mosaic disease. The supporters 



