46 BULLETIN 1256, U. S. DEPARTMENT OF AGRICULTURE. 



poses. This condition has been attributed in some southern dis- 

 tricts to the action of an insect (thrips) feeding on the veins of 

 the leaf in the field, with the result that when cured these become 

 much lighter in color than the remainder of the leaf. 



In the northern districts white veins appear occasionally, ap- 

 parently as a result of excessively rapid curing of the leaf during 

 dry weather. It is believed that the surface layers of the veins, 

 drying out more rapidly than the deeper layers of tissue, permit a 

 thin layer of air to form between the two layers, thus causing the 

 veins to appear white. In any case it is a good plan to keep up 

 the humidity of the shed in dry weather by keeping the shed closed 

 in the daytime, opening it partly at night, and occasionally apply- 

 ing water to the ground in the shed to raise the humidity of the 

 inside air. 



BLACK-ROT IN FERMENTATION. 



Description. — Following curing, tobacco is ordinarily graded and 

 bulked in various ways, depending upon the type, when it is suffi- 

 ciently pliable for handling without breakage. Leaf tobacco of 

 manufacturing types is usually " reordered " to bring it to the 

 2:>roper moisture content before storage, and damage rarely occurs. 

 Leaf tobacco of cigar types, however, is usually allowed to come 

 into higher " case " before being removed from the curing barn, with 

 the result that it often contains a high percentage of moisture, and, 

 moreover, it is not " reordered " before packing in boxes for fer- 

 mentation or sweating. 



Black-rot is ordinarily found, then, in boxed cigar types of to- 

 bacco. It usually appears as a dark-brown or black discoloration 

 of the packed tobacco, which varies from only small insignificant 

 local areas on a few leaves to almost complete ruin of the entire lot. 

 Commonly the affected area is more or less limited to the tip ends 

 of the leaf where they OA^erlap in packing. The affected tissue is 

 ordinarily characterized by a dry rot, and the body, texture, and 

 elasticity of the leaf no longer exist, and it easily breaks up when 

 disturbed (PL XVII, fig. 1). Commonly a sooty appearance is pres- 

 ent, as a result of the production of large numbers of spores by the 

 organism causing the decay. The line of demarcation between rotted 

 and sound areas is frequently quite sharp, and the sound portions of 

 the leaf are still of value for cigar purposes if large enough to war- 

 rant their separation. Sometimes black-rot appears in bundled 

 tobacco before sorting. The loss from this trouble is frequently 

 quite large in the packing houses of northern cigar-tobacco districts. 



Cause. — Black-rot has been found to be due to a fungus common 

 in nature, Sterigmatocystis nigra, more often called Aspergillus 

 nir/er. This fungus is peculiar in that it thrives best at relatively 

 high temperatures (around 100° F.), such as exist in fermenting to- 

 bacco. It can also grow, of course, at considerably lower and slight lv 

 higher temperatures. 



The fungus produces spores abundantly, which can remain dor- 

 mant for a long time, arc readily carried about in the air, and arc 

 quite common in tobacco warehouses. When these spores are present 

 on tobacco they can germinate under favorable conditions and pro- 

 duce decay of leaf tissue in a few days. 



