MR. SOLLY OX TUK POTATO MURRAIN. 39 



from a statement made in Ireland of a lambent phosphorescent 

 light having been observed playing over a large field of potatoes 

 one night, which a few days subsequently were fomid to be at- 

 tacked by the disease. It is most probable in this case, that the 

 light observed was that luminous effect frequently seen when 

 organic matter is decaying, and that the potatoes were in fact 

 already decaying when the light was noticed. The luminosity 

 of decaying potatoes has been frequently remarked, and strong 

 phosphorescence has even been observed from sound potatoes in a 

 state of germination. 



The third and fourth of the theories quoted, may properly be 

 considered together, being in fact closely connected. It is well 

 known that at a certain period of the year there was a remark- 

 able deficiency of heat and light, and consequently tiie chemical 

 fiuictions of the plant must have gone on but languidly at that 

 time ; but there is no evidence to show that the vitality of the 

 plant was in any way weakened ; on the contrary, it appears 

 from several circumstances that the plants were far from deficient 

 in vitality. It lias been supposed that the rot Mas a mere effect 

 of oxidation or eremacausis, the oxygen of the air burning^ the 

 vegetable tissue in consequence of the decreased vitality of the 

 plants being no longer able to withstand its action ; this explana- 

 tion however is not only rendered improbable by the great vitality 

 of the plants, but also by the fact that in the earliest stage of the 

 disease it is scarcely at all accelerated by the action of an atmos- 

 phere of moist oxygen gas, which, were this explanation correct, 

 ought to increase the decays rapidly. 



It has also been stated, that the disease was caused by oxida- 

 tion of the tissues in consequence of their being thin and imper- 

 fectly formed ; this alone, however, could not account for their 

 decay, unless the vitality of the plant likewise were feeble, a 

 condition not generally accompanying rapid and vigorous 

 growth. The cellular tissues of the potatoes were quite as per- 

 fect and complete as the cellular tissues of young plants, and the 

 young and freshly formed ports of a healthy plant do not exhibit 

 any tendency to putrefy or decay from mere oxidation ; in fact, 

 if the mere presence of a large quantity of water and excessive 

 permeability of the membranes were the causes of the disease, all 

 young tubers would be exceedingly liable to it, as they contain a 

 very high proportion of water, and their cells are but imperfectly 

 formed. 



After a careful examination of the various arguments which 

 have from time to time been brought forward in support of the 

 different theories, and an attentive consideration of the fiicts of 

 the case, I must confess myself still of the .same opinion which I 



