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he believes it to be a fact that it could not establish itself on a decayed 

 substance. The parasitical fungus, botrytis infestans, is, therefore, to my 

 mind, most unquestionably the immediate cause of the potatoe blight. — 

 It is well known to be a power perfectly adequate to accomplish the eflfect 

 under certain conditions. 



It may be well to notice the chief objections which have been urged 

 against this explanation. Many assert that fungi have not the power to 

 destroy plants : and even well-informed men, certainly not botanists, but 

 men having some pretensions to scientific knowledge, have said that 

 fungi prey upon decaying matter only, therefore, it is to them incompre- 

 hensible how they could possibly cause the disease. But instead of prov- 

 ing the fungal theory to be erroneous by such statements, they only 

 proved their own ignorance of facts of every-day occurrence, for no 

 truth can be better established, than that some species of fungi do 

 attack plants before there has been any visible appearance of decay, that 

 they spring from the living tissue and destroy it. 



Others have said that in order to have produced the disease of 1845, 

 the fungus must have attacked every plant, and some fields in an 

 unhealthy condition were examined, without finding the least trace of it. 

 I have noticed fields of potatoes in a diseased state which was obviously 

 not due to the fungus ; the symptoms were altogether different. But 

 then, I have examined field after field for miles, attacked by the mildew ; 

 I. have seen the parasite commencing its ravages ; I have seen crops, 

 which at the first glance, presented an uniform healthy appearance, when 

 the lower leaves on examination were found to be attacked by the para- 

 site. And because, I have met with instances of disease not apparently 

 caused by the fungus, am I then to conclude, despite the evidence of my 

 own senses, and of the testimony of observers like Berkeley and Morren, 

 that the fungus, botrytis infestans, is not the immediate cause of the 

 blight ? The only conclusion that I feel justified in arriving at, is, that 

 another disease co-exists with that of the blight. The potatoe has, indeed, 

 been afi'ected by several distinct diseases of late years, and it is owing to 

 the want of a knowledge of this, and to the vain attempt to find one 

 cause, which will account for all the forms of disease that have tended 

 so much to perplex the question. If cholera was decimating the popu- 

 lation of a country, and a man were to find in certain localities, cases of 

 typhus and scarlatina, would it be considered a valid objection that 



