STUDIES ON THE CURING OF LEAF TOBACCO. 35 



treated clearly show that normal curing does not take place. Since 

 these normal changes in composition are effected by hydrolytic 

 enzyms, and since it is well known that the green leaves of plants 

 normally contain these enzyms, it is not clear why protoplasmic 

 poisons which do not inhibit the action of such enzyms should 

 prevent the progress of the curing along these lines. Brown and 

 Morris * considered this matter in connection with their investigations 

 on the occurrence of diastase in the leaves of plants, but did not 

 arrive at a satisfactory conclusion. They found that, although the 

 diastatic activity of the leaf increases markedly when it is kept in 

 darkness, even when a leaf has been subjected to this treatment 

 there is no further decrease of starch after treatment with chloroform. 

 Whatever the explanation of this phenomenon, it seems logical, as 

 suggested by Brown and Morris, that partial starvation will lead to 

 an increased formation by the leaf cell of enzyms designed to furnish 

 the needed nourishment. We have found that such is the case as 

 regards diastase in the curing of tobacco leaves. The method used 

 for comparing the diastatic activity of fresh and partially cured 

 leaves was that described by the above-named investigators, and 

 consists essentially in digesting a given weight of the material with 

 a 2 per cent water solution of soluble starch under proper conditions 

 and with suitable controls. The increase in reducing sugars is 

 taken as a measure of the relative diastatic activity. 



In the following experiments, after having obtained the leaf areas, 

 one half of each leaf was chloroformed and dried at 35° C, while 

 the remaining half of each leaf was maintained under normal curing 

 conditions (slow drying in darkness and at moderate temperatures) 

 for a period of 43 hours in experiment 1 and for one week in experi- 

 ment 2. 



The material chosen for the first experiment was a single mature 

 bottom leaf taken from a Connecticut Broadleaf plant grown in 

 the greenhouse, and in the second experiment one bottom and two 

 top leaves were taken from a mature plant of Yellow Pryor grown 

 under normal field conditions. The cured material was chloroformed 

 and dried in the same manner as the uncured. The diastatic activity 

 was determined for equal areas and not equal weights of the cured 

 and uncured material, and the results as reported are in terms of 

 the weights of maltose formed by digesting 10 grams of the uncured 

 samples chosen as standards and weights corresponding to an 

 equal area of the other samples with 2 per cent soluble starch solu- 

 tion for 48 hours at 30° C. It is necessary to use equal areas of leaf 

 to correct properly for the loss in dry weight in curing. The results 

 of these experiments are shown in Table VIII. 



i Brown, H. T., and Morris, G. H. Contribution to the chemistry and physiology of foliage leaves. 

 Journal, Chemical Society [London], Transactions, v. 63, p. 604-659, 1893. 



