The Potatoe Plague. 73 



the germinating seed, which diastase assists in the conver- 

 sion of starch into the gum, sugar, &e., which are required 

 for the nourishment of the young- shoot. The potatoe con- 

 tains a very small per centage of nitrogenous matter. I 

 would, therefore, venture the suggestion that the great addi- 

 tion made in the process of ripening, to the already large stock 

 of starch contained in the tuber, may be more than can be 

 converted into the gum, sugar, &c., by the small quantity of 

 diastase generated in the germinating potatoe. If this be the 

 case, then it would follow that the diastase being mixed with 

 too large a proportion of starch (like leaven mixed with too 

 large a proportion of dough) only does its work imperfectly, 

 and the result is a weakly shobt, whilst a portion of the 

 starch, failing to receive the vitalizing influence of the dias- 

 tase, undergoes the natural course of decay, and produces the 

 symptoms peculiar to dry-rot, wet-rot, or curl. This suppo- 

 sition is, of course, pure theory, and must not be confounded 

 with the facts on which it is based. To make it quite clear 

 where the one ends and the other begins, I will very briefly 

 recapitulate. Facts have been brought forward to prove that 

 ripe sets are subject to curl, and vice versa, also that a large 

 addition is made to the quantity of starch in the potatoe in 

 the process of ripening. Direct experiment also proves that 

 " diastase " is required for the germination of seeds, which 

 diastase can only be formed from some substance containing 

 nitrogen ; potatoes contain a very small proportion of such sub- 

 stances, and therefore can have but very little diastase. Here 

 our facts end, but from these premises I would hazard the 

 deduction that if we allow our seed potatoes to ripen, they 

 acquire more starch than can be made available to the grow- 

 ing shoot ; which excess naturally decays, and then infects 

 and injures, or even destroys, the plant with which it is con- 

 nected. A similar effect is produced in the human subject 

 when more food is taken into the stomach than the gastric 

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