SCIENCE IN ITS APPLICATION. 97 



soggy and easily torn lot of leaves, hopelessly damaged. 

 Dr. Win. C. Sturgis,* in describing this disease, says : 

 "It is characterized by the appearance on the surface of 

 the leaf, of small blackened areas, giving the leaf the 

 aspect of having been sprinkled with some corrosive liquid. 

 . . . These areas increase in size, become confluent, 

 and sometimes within thirty-six hours, or at most, forty- 

 eight, not only is the whole leaf affected, but the entire 

 contents of the curing barn may be rendered quite 

 worthless as tobacco. Microscopic study revealed in the 

 center of each blackened spot a minute, elevated pustule. 

 Sections through the center of one of these pustules 

 showed that the tissue of the leaf was largely disinte- 

 grated, and the cells themselves were largely filled with 

 bacteria. . . . They develop rapidly in the tissues 

 of the leaf, raising the epidermis, and finally breaking 

 through at one or more points in the blackened area, 

 . . . they spread out in a thin, slimy film, . . . 

 forming a brown, translucent crust of cheesy consistency, 

 and composed entirely of the bacteria themselves." 



In tracing the development of the disease, this au- 

 thor states that, at first, the surface of the leaf is at- 

 tacked by a fungus of the genus Cladosporium, related 

 to the leaf-spot disease of the tomato. This does little 

 direct injury, but after some time the leaf is attacked by 

 the bacteria, which swarm into the interior through the 

 breaches made by the Cladosporium, the remains of 

 which are found mingled with the bacteria. Of the lat- 

 ter, there are, at least, two species, one a true Bacteri- 

 um, the other a Micrococcus, of the variety Streptococcus. 



These bacteria develop best between 70 and 90 F., 

 but a temperature above 90 to 110, or below 35 to 40, 

 checks their development. Furthermore, all attempts 

 to inoculate the cured tobacco with them failed ; the 



* Report of the Connecticut Ag. Exp. Sta., 1891, pp. 168-186. 



7 



