2 BULLETIN 19, U. S. DEPARTMENT OF AGRICULTURE. 



manner in the barn. There is an important modification of the 

 method of harvesting and curing the leaves on the stalk in that, 

 prior to being severed near the base, the stalk is split longitudinally 

 from the top down the greater part of its length and when cut is 

 placed astride a stick for hanging in the barn. 



NATURE OF THE CURING PROCESS. 



Observant growers well know that tobacco leaves which have been 

 killed by freezing or by bruising do not cure normally, and a leaf 

 which is quickly dried by heat does not possess the properties of 

 the cured leaf. Moreover, if the fresh leaf is subjected for a few 

 minutes to the action of protoplasmic poisons, such as formaldehyde 

 or chloroform, it will not cure properly. It is quite evident, therefore, 

 that curing is a life process and thus differs fundamentally from the 

 subsequent fermentation, which takes place after the death of the 

 leaf cells. That curing is essentially a life process can also be readily 

 shown by chemical analysis, as is brought out in later paragraphs. 



Curing materially changes the physical and chemical properties 

 of the tobacco leaf, more particularly such properties or qualities 

 as the capacity to hold fire, the color, the texture, and the elasticity. 

 It does not develop the aroma, however. With respect to the 

 development of some of the above-mentioned properties of the leaf, 

 fermentation may be regarded as supplementary to curing; but, as we 

 hope to show more fully in a later publication, some of the important 

 changes in composition involved in curing are not continued in the 

 fermentation, so that incomplete curing can not be fully corrected 

 in the subsequent fermentation. 



As will be shown later, curing involves principally the two familiar 

 physiological processes of respiration and of the translocation of 

 mobile nutrients. Some investigators have preferred to regard the 

 respiration phenomena as essentially pathological in character, and 

 this view seems logically correct. The stalk and its leaves or the 

 leaves alone, as the case may be, after harvesting are deprived of the 

 water solution from the root system and for the most part are de- 

 prived of sunlight. Since respiration continues, the living cells of 

 the leaf are subjected to a process of starvation, and the degree to 

 which the starvation proceeds is largely dependent on the rate of 

 drying. As a matter of fact, however, the general character of the 

 changes in composition during the curing, due to respiration, is very 

 much the same as in normal respiration. As would be expected, the 

 prevailing temperature and humidity play an important r61e in the 

 process. The other important phenomenon, translocation, involves 

 the movement of soluble materials from the leaf web, through the 

 veins, into the midrib, and, if the leaf is attached to the stalk, thence 

 into the latter. With one or two exceptions, investigators have over- 



