MR. SOLLY ON THE POTATO MLKKAIX. 



37 



present any marked peculiarities, further than that the percentage 

 of fibre was rather lower than usual, whilst that of water was 

 decidedly above the usual average. In the decaying tubers there 

 was also found more water, but less azotised matter and less fibre 

 than usual ; a considerable quantity of free ammonia, and traces 

 of sulphuretted hydrogen being also present. As might have 

 been expected, those parts in the vicinity of the eyes were 

 generally the first to change, the ordinary effects of germination 

 being apparent along with those of the diseased ; hence in those 

 parts the starch was partially converted into sugar, at the same 

 time that the cellular and azotised matters putrefied. The 

 following shows the relati\'e proportion of the organic con- 

 stituents -of sound bread-fruit potatoes of last year, and two 

 preceding seasons. 



Starch .... 



Fibre .... 



Gum and resin 



Soluble azotised matter — albunieu 

 Insoluble azotised matter — gluten 

 Water .... 



10000 10000 10000 



From these few facts it is evident that the disease is a putrid 

 fermentation, or '• mortification," of the organic matter of the 

 plant ; the question then arises, what was the cause of this fer- 

 mentation ? The effect M'as clearly a chemical change, a reso- 

 lution of organic substances into simpler forms of matter ; and 

 accordingly it is reasonable to expect that some definite chemical 

 cause may be found to which these efl'ects can be traced. Vari- 

 ous theories have been proposed to account for the origin of this 

 putrid matter : the most plausible, or at least the most strongly 

 supported of these views are — 1, That it is caused by fungi ; 

 2, by electricity; 3, by simple eremacausis or excolation, in con- 

 sequence of deficiency of vital energy in the plant; 4, by defi- 

 ciency of light and heat. Besides these, several other theories 

 have been suggested, of which it is unnecessary to speak, as the 

 effect is evidently mistaken for the cause. I will now endeavour 

 to show in how far their several views are sufficient to account for 

 the chemical cfiect produced. 



It has been stated, and that by some of the highest authori- 

 ties, that the disease is caused by the growth of microscopic fungi. 

 That they exist in enormous numbers in the diseased potato, 

 as indeed they do in almost all forms of decaying organic matter, 

 cannot be doubted ; but that they could possibly alone cause such 

 a disease as that which has this season manifested itself in the po- 

 tatoes, seems to me to be incomprehensible ; we must at the 



