26 MR. BERKELEY ON THE POTATO MTJRKAIN. 



various species of fungi should establish themselves upon the 

 tubers and accelerate it. It is well known, without having re- 

 course to the curious observations of Dr. Nageli,* tliat various 

 funoi do exist in the tissues of plants, accelerating their decom- 

 position. A very singular species will be described at the end 

 of this memoir. Facts of this kind, wliether we observe them 

 or not, are daily before our eyes, and there would be little diffi- 

 culty in admitting that the decay of the tubers was produced by 

 natural decomposition arising from their imperfect organization, 

 the tubers being unliealthy from various outward circumstances 

 and from the premature decay of the haulm, but for the curious 

 fact that the same mould which s[)rings from the substance of the 

 leaves, uniformly bursts forth from tlie tubers exactly at the very 

 spots where the decay originates. That the mould proceeds 

 from within I can assert from personal observation, and believe 

 it to be a fact that it could not establish itself on a decayed sub- 

 stance ; nor, indeed, have my experiments been successful as 

 regards sound tubers. Portions of the mould transferred to 

 healthy tubers placed in favourable situations for its growtli have 

 remained precisely in the same condition, without establishing 

 themselves in their new situation, and inoculation has not at 

 present been attended with any positive result. It should seem 

 certain, then, that the mycelium or elements of the fung-us must 

 have pre-existed in the tuber ; and as it uniformly springs from 

 the decayed spots, that it has itself caused the decay. 



But here a difficulty arises from the great obscurity, or as 

 some say, the total absence of mycelium in an early stage of the 

 disease. I have satisfied myself however of its existence in some 

 cases, but not uniformly. Another difficulty arises from the 

 fact that diseased tul^ers are found occasionally on plants whose 

 foliage is untouched,! or only slightly affected by the mould. 

 The disease in tliis case at least does not arise from tlie dete- 

 rioration of the tuber from tlie decay of the foliage. But if, 

 previous to the breaking out of tlie mould from the leaf, the 

 cellular tissue is impregnated with mycelium, a fact which I 

 have had no opportunity of ascertaining since my observations 

 were commenced, it is possible enough that it may be present in 

 the tubers which are leafless branches, and if so, it may exercise 

 its influence on the tuber before it bursts forth from the leaf. 

 And if these observations be well grounded, the case is merely 

 an exceptional one. In those cases in which I have myself 

 found diseased tubers while the foliage was still more or less 



* Linnsea, vol. 16, p. 237. 



t Decaisne, Rev. Bot., 1845, p. 150. 



