38 ME. SOLLY ON THE POTATO JIURRAIN. 



outset be led to ask, why there should be such an immense deve- 

 lopment of fungi this year, above all previous years? and the 

 only legitimate answer to this question appears to be, that the 

 plants were to a certain extent in a diseased state, which favoured 

 the growth of the fungi. In stating that the fungi were the 

 cause, we in truth only express the fact in a new and rather ob- 

 jectionable form ; because then the main question is merely 

 resolved into — What was the cause which led to such an ex- 

 traordinary growth of fungi. The term however is objection- 

 able, because there is no evidence tliat fungi have the power of 

 inducing putrefaction ; on the contrary, all chemical evidence 

 would lead us to an opposite conclusion, viz., tliat fungi grow in 

 putrefying organic matters because they there find abundance of 

 those substances on which tliey live. When a number of solu- 

 tions of animal matter are placed in the circraustances most 

 favourable to putrefaction and the development of fungi, it is 

 always found tliat fungi grow and flourish in some, whilst the 

 other solutions are free from them, being in fact only developed 

 in those which are in that state of putrefaction favourable to their 

 growth ; moreover, they do not appear until the solution has 

 acquired that state. Again, organic matter placed in tliose con- 

 ditions necessary to the growth of fmigi, and properly inoculated 

 with them, the conditions requisite to decay being excluded, do 

 not decay even though the fungi grow. Fungi never gi'ow 

 except in decaying organic matter, but decay frequently exists 

 when no fungi are present. 



As far as my own microscopic observations enabled me to form 

 any judgment, the growth of the fungi followed but never pre- 

 ceded the decay of the potato — it was the result but not the cause. 

 At the same time, however, there is no doubt wliatever that the 

 growth of fungi does accelerate those changes wliich constitute 

 decomposition, both chemically and also meclianically, by loosen- 

 ing the adiiesion of tlie cells and destroying the continuity of the 

 vegetable membranes. 



The statement that the disease was caused by electricity, appears 

 to have been unsupported by any evidence, and merely thrown 

 out as a possible thing ; a very little consideration will show its 

 extreme improbability. Plants growing in the free and open 

 fields miglit possibly be affected by a deficiency or excess of at- 

 mospheric electricity ; but supposing that they were so, it is 

 evident that those wliich grew under the shadow of trees, and in 

 other situations where they must be protected from the influ- 

 ence of free electricity, would not be so affected. Now it was 

 found this year that the vicinity of trees, &c. did not in any way 

 diminish or increase the effects of the disease. An argument 

 in favour of the electric theory was endeavoured to be drawn 



