PRESENT DISEASE IN THE POTATOE. 33 



In this case the destruction of the plant is not referable to 

 a new infection, but to the previous existence of disease in 

 the plant ; and thus we find that a diseased portion of a 

 plant is very apt to cause the disease in all future growths 

 emanating therefrom. 



(126.) On account of this continuous propagation of the 

 disorder, it requires much care at the present time to de- 

 termine the spot at which the first action of the disease 

 takes place ; or, in other words, to ascertain whether the 

 plant be primarily affected at the leaves or at the tuberose 

 stems. From the results of all my experience, I believe 

 that the primary effect is more generally first noticed at the 

 upper stem, but that a diseased tuber tends greatly to the 

 destruction of a plant by the changes occurring in the stem 

 below the surface. 



(127.) Notwithstanding innumerable investigations upon 

 this point, I wish to speak with great caution ; and, in fact, 

 it is but of little consequence whether the effect of the dis- 

 ease is shown at the upper or lower parts of the plant in 

 the first instance, as there can be no doubt that the malady 

 severely injures the entire plant, in whatever part it may 

 originate. 



(128.) The mere local changes in the plant, or dead 

 portions which we perceive, are the results of the malady : 

 the disease itself attacks the entire plant, and, therefore, 

 the mere local changes are really of no great importance. 

 The disease cannot be said to reside in the blotch in the 

 leaf, the dead part of the stem, or in the rotten potatoe : it 

 is a far more recondite affair, having its residence in the 

 vital elements of the plant ; and, therefore, we may infer 

 that it is a disease connected with the sap and cellular 

 tissue, and thereby influencing the vital actions which oc- 



2* 



