288 MASSACHUSETTS AGRICULTURE. 



be engendered. A communication by contagion might still 

 be but one among a great number of exciting causes, not 

 bearing any relation to the original cause of the disease. 



II. The predisposition to disease may be hereditary. Of this 

 there seems to be no good reason to doubt ; but admitting it as 

 a fact, may we not, by a series of careful experiments, discover 

 the means by which it is most likely to be communicated from 

 one crop to the succeeding one ? In order to put this supposi- 

 tion to the test, let a field of uniform soil and situation be 

 divided, like the foregoing, into equal parts ; then select from 

 the same kind and the same lot of potatoes, one portion 'entirely 

 sound for one division, and another portion of diseased tubers 

 to be planted in the other division. Let the ground be prepared 

 and manured in the same way for each, and let the two crops 

 be cultivated in exactly the same manner. The sound potatoes 

 would probably yield the largest crop ; but the object of the 

 experiment should be to ascertain whether a diseased tuber 

 necessarily yields a diseased product. 



The preceding experiment may be modified in the following 

 manner: Let the two sections of a field, prepared as before, 

 be planted each with sound potatoes of the same variety ; but 

 let the seed for one section be selected from a crop which has 

 not manifested the disease, or at least only in a very slight 

 degree ; and let the seed for the other section be also sound, 

 but selected from a crop which was very much diseased. Take 

 notice whether, under these circumstances, one is more affected 

 than the other with the malady. It may turn out— though 

 such a supposition is very improbable — that it is best to select 

 seed potatoes from among the sound ones of a diseased^crop, on 

 the supposition that they must possess the property of resisting 

 disease in a remarkable degree, and might communicate this 

 power of resistance to their offspring. We know that such a 

 principle exists in the animal constitution, to a certain extent ; 

 but this is not a problem to be solved by reasoning ; it must be 

 settled by experiment. It is important, however, to ascertain 

 whether a crop produced by sound potatoes from a sound lot, is 

 more likely to be exempt from the malady than one produced 

 by equally sound potatoes from a diseased lot. 



III. A third course of experiments should be designed to 

 ascertain the effects of certain modes and materials of fertiliza- 



