324 Transactions of the Canadian Institute. [Vol. V'II. 



green colour naturally ; and one species of the genus has its specific 

 name from this character. 



About the time that Dr. Mayer was carrying on his investigations in 

 Holland, a disease was described which occurred in South Eastern 

 Russia which resembled very closely the " calico " of America. Some 

 examination was made in detail as to the nature of the disease, as it was 

 called, and the conclusions reached were that the cause was not due to 

 bacteria nor to enzymes, and was therefore in no sense what might be 

 termed an organic disease, but entirely physiological in its nature. 

 It was proved by experiment (^Sturgis, 1898) that the lower leaves of a 

 tobacco plant will become spotted when the plant is beginning to starve 

 because of a lack of water; and it occurs similarly when a period of 

 excessive humidity is followed by hot sunshine, which results in a very 

 rapid transpiration. It was, moreover, asserted by some, that spots 

 were produced by drops of water adhering to the leaves and acting as 

 lenses, and in direct sunlight actually burning the leaf. This is 

 probably not true, as tobacco is not one of those plants to whose leaves 

 the water adheres in drops ; besides we are unable to bring this about 

 by artificial means upon this plant. Others state that particles of sand, 

 dust, etc., will, when adhering to the leaf, cause a " speck " to be 

 produced as a result of the contact and the irritation brought about by 

 the particle. This is quite probably not correct unless the particle 

 adhering acts chemically upon the leaf cutin and the cells and their 

 contents. It may be that where the land was fertilized freely with 

 ashes, lime, or other rather strongly alkaline substances there is a 

 modicum of truth in the statement ; and indeed this would tend to 

 confirm the assertion that the spotting of the Sumatra leaf is due to 

 wood ashes brought into actual contact with the leaves by means of the 

 wind. 



A few years ago Marchal described a disease of the tobacco, similar 

 to " calico." He concluded that it was a bacterial disease, as he saw 

 in the spots a bacillus which he was able to grow upon pure culture 

 media, and in turn to inoculate healthy plants with the pure culture. 

 Others have found since Marchal's investigations were made that the 

 mottling is due to a sort of enz}'mitic action. Now it is obvious that 

 these so called diseases, " mottled-head," " Mosaic disease," " calico," 

 etc., are distinguishable in a general way from the " Tobacco Spot " 

 which is so universally admired in a cigar wrapper ; and that so 

 far as investigations have been made upon the subject up to this 

 time, it may be regarded that "Tobacco Spot" is a physiological 



