18 ME. BERKELEY ON THE POTATO MUEEAIX. 



bruised, on which there is a minute mucor. It is plain, that at 

 a late period of the disease, when other fungi have been estab- 

 lished, and on breaking the tuber mucedinous patches are visible 

 within, all traces of the original parasite may easily be lost. 

 But even in this state it should seem that there is some difficulty 

 occasionally in tracing any mycelium amongst the cells, as 

 Monsieur Desmazieres, a most practised microscopic observer, 

 had not, even so late as the 17th of January — though the tubers 

 he examined were eaten up with a Fusarium — been able to detect 

 any mycelium. 



The order of phenomena described above is such as to show a 

 very intimate connection between the parasite and the disease. 

 Accordingly, the notion that the disease is the effect of the para- 

 site has met with some advocates, especially in Belgium. Mon- 

 sieur Payen also, to a greater or less extent, accords with Dr. 

 Morren : and, after an attentive consideration of the progress of 

 the disease and of almost everything of value that has been 

 written on the subject, and after duly weighing the peculiar diffi- 

 culties with which it is attended, I must candidly confess, that 

 with a becoming share of philosophic doubt where such authori- 

 ties are ranged upon tlie opposite side,* 1 believe the fungal theory 

 to be the Irue one. I cannot claim the support here of my 

 friend Dr. Montague, though he has been imagined by some of 

 his colleagues to accord in opinion with Dr. Morren ; but in 

 the very first conmiunication I had from him upon the subject 

 he expressly stated his fioubts as to the true cause of tlie disease, 

 though at the same time he admitted its intimate connection 

 with parasitic fungi. 



To avoid going twice over the same ground, it will be con- 

 venient to consider first the other opinions which have been 

 brought forward. 



The principal advocates of the opinion that the disease is in 

 the first instance independent of parasitic fungi, and that it arises 

 from the peculiar atmospheric conditions of the season, are the 

 members of the Brussels and Groningen Commissions ; Dr. 

 George, Dr. Vallez, and De Potter, in Belgium; Bouchardat, 



* Monsieur Dueliartre, in the 'Revue Botanique,' 1845, p. 177, states that 

 I have modified the uotious which I at first entertained of the Botrytis being 

 the cause of the disease, founding this assertion on my correspondence with 

 Dr. Montague. There is certainly some mistake in this. I may have ex- 

 pressed myself as open to conviction, and acknowledged, as I still do, the 

 difficulties of the case ; but at present I have certainly seen no reason to 

 depart from the opinion I formed from the moment I had an opportunity of 

 examining the matter for myself. My first communication to the ' Gar- 

 dener's Chronicle' was made before I had an opportunity of seeing the disease 

 in situ. 



