PRESENT DISEASE IN THE POTATOE. 35 



cause should not continue to act, the malady would be 

 gradually annihilated. 



(133.) I have had abundant opportunity, nevertheless, 

 of observing, on the other hand, that potatoe plants which 

 are the offspring of formerly infected tubers manifest the 

 disease without the intervention of the cause which first 

 produced it, and which I shall hereafter point out. 



(134.) The disease affects plants at all periods of their 

 age, from the newest seedling to the oldest variety. There 

 is, however, a difference in different kinds in this respect ; 

 and in a field where many kinds of potatoes are planted, a 

 considerable variety is observable in the mode in which the 

 plant is attacked. 



(135.) It affects plants also in all periods of their growth. 

 I have seen it in a plant where tubers have been formed 

 without haulm ; I have seen it where the stem has not 

 exceeded three inches in height ; and I have seen it in 

 more mature plants. 



(136.) The examination of the diseased tuber presents 

 very interesting matter. In the first place, we observe the 

 potatoe in some instances to have an undue hardness to the 

 feel ; in this case, where a thin section is examined under 

 the microscope, the cells will show but a small quantity of 

 starch, the granules will be but few, and in some cases 

 merely rudimentary. (Plate vn., fig. 7.) 



(137.) At a later stage we may observe these cells 

 breaking up into a brownish material, and losing their 

 perfect cellular character. We perceive, also, fine lines 

 crossing the cellular tissue here and there, phenomena to 

 which I shall hereafter more particularly draw attention. 



(138.) When the decomposition is more advanced, and 

 the plant takes on a more fluid condition, we find starch 



