STUDIES ON THE CURING OF LEAF TOBACCO. 33 



these constituents were transported from the leaf into the stalk 

 during the process of curing. It is evident that the phenomena of 

 translocation in the curing of tobacco leaves attached to the stalk 

 follow essentially the same laws as obtain during the growth and 

 development of plants under normal conditions. The movement of 

 reserve nutrients is from the leaf web through the veins and midrib 

 into the stalk and normally thence to the younger growing parts. 

 Only such constituents as are the most essential, physiologically, 

 undergo translocation to a marked degree. 



ENZYMS IN TOBACCO CURING. 



It has been pointed out in the preceding pages that tobacco curing 

 consists, primarily, in the hydrolysis of insoluble carbohydrates and 

 proteins, followed by a partial or complete removal of the cleavage 

 products by further hydrolysis and by oxidation and, in stalk curing, 

 by translocation into the stalk. It is quite generally recognized that 

 the immediate agencies effecting transformations of this character 

 in the vital activities of the plant are enzyms. We have shown that 

 starch and pentosans are converted into reducing sugars, which are 

 then oxidized or translocated, and that protein is converted into the 

 simpler amid or amido derivatives, from which, in turn, ammonia is 

 split off. It seems probable, therefore, that diastases, cytases, and 

 proteolytic and deamidizing enzyms take part in the curing of the 

 tobacco leaf. It seems very probable also that the oxidases play an 

 important part, particularly as regards the changes in color which 

 the leaf undergoes in curing. 



We have not attempted to go into a study of the enzyms concerned 

 in tobacco curing, except simply to bring out the fact that their 

 activities are for the most part intimately associated with and de- 

 pendent upon the presence of the living protoplasm. We have 

 already pointed out that a ripe tobacco leaf will not cure properly, 

 even under the most favorable conditions, if it has been previously 

 subjected to very high or low temperatures or to the action of pro- 

 toplasmic poisons. It has also been stated that the progress of the 

 curing can be readily followed by determining at different stages the 

 relative quantities of unchanged starch and protein contained in the 

 leaf. The following experiments show by chemical methods that 

 the premature killing of the protoplasm prevents the changes in 

 composition which are essential to successful curing. 



In the first place, an experiment was carried out to determine the 

 effectiveness of rapid drying at high temperatures in preventing these 

 changes in composition. Two lots of leaves, containing 14 leaves in 

 each lot, were selected in the manner described on page 4, and one 

 of these lots was allowed to cure normally. The midribs were re- 



