AND FARMING PRODUCE. 319 



until the tuber is thoroughly converted into a 

 brown morbid mass. 



From numerous failures during the winters of 

 1845 and 1846, in attempts to infect sound tubers 

 with the sporules of the fungi it seems that the 

 disease cannot be communicated by them. In all 

 cases observed, the disease has commenced before 

 they make their appearance. And as it is the 

 special office of all these parasites, by preying 

 upon diseased and dead vegetable structures and 

 organs, to remove what has become useless for 

 vital and healthy purposes, and inert, because 

 defunct, in order that their elements may enter 

 speedily into more active and vigorous combina- 

 tions, these fungi cannot for this reason be con- 

 sidered as the cause, but the consequence of the 

 disease. I have seen tubers wholly infected 

 without the slightest vestige of a fungus ; yet, far 

 as I recollect, such tubers were infected by others, 

 and not those which had the disease engendered 

 within themselves. 



During the last winter, I have repeatedly 

 inocculated ripe sound tubers with the virulent 

 matter of the murrain, and thereby induced the 

 disease. This may account for the spread of the 



