16 MR. BERKELEY ON THE POTATO MURRAIN. 



the same mould which destroyed the leaves springs from them, 

 piercing the cuticle from within, yet not scattered, as on the 

 leaves, but forming a conspicuous white tuft. If a section of the 

 diseased tuber be made on the first symptoms of the disease, little 

 brownish or rusty specks are found in the cellular tissue, con- 

 fined, with very rare exceptions, to the space between the 

 cuticle and the sac, if I may so call it, of spiral vessels and their 

 accompanying tissue, which, springing from the subterranean 

 branches, pass into the tuber, making their way to the several 

 buds disposed on the surface. The disease, I believe, commences 

 in the mother cells of the fecula, and not in the empty subcu- 

 ticular cells, or in the cuticle itself, though the contrary has 

 frequently been stated. These spots consist at first of a quantity 

 of discoloured cells mixed more or less with others in a healthy 

 condition. The walls are tinged with brown, and sprinkled both 

 within and without with extremely minute inorganic granules, 

 which Monsieur Decaisne* has found to resist the action even of 

 concentrated boiling muriatic acid. The grains of fecula, 

 which are themselves sometimes powdered with the brown bodies, 

 are for a long time perfectly healthy, without any laceration of 

 their walls or change of colour, and are never, as in tlie disease 

 of Martins, rough witli incipient fungi. The cells themselves, 

 so far from being looser, are more closely bound together than 

 in the more healthy portions. In general, no traces of mycelium 

 are visible in this stage, but I have found in the midst of the 

 patches in some of the cells, usually in those less diseased, young 

 plants of mould springing from the walls within, exactly as 

 Martiusl has figured the incipient Fusarium in the disease which 

 he has called Dry Rot. The processes on the cells, which 

 Payen took for mycelium, exist not only on the diseased cells or 

 on the sounder cells of the diseased tubers, but I have found 

 them also in potatoes of 1844, and in tubers produced from 

 them in the cellar ; and there appears to be something analogous 

 on the mother cells of other plants, as in those of the tulip and 

 Arum maculatum. Their resemblance, however, to mycelium, 

 from their mode of growth, and occasionally somewhat dicho- 

 tomous habit, is so strong that it is very difficult to divest oneself 

 of the notion that they are really of a mucedinous character, 

 especially when Payen's chemical analysis, corresponding so 

 closely with that of fungi, is taken into consideration. J The 

 rusty spots soon exhibit a darker tint, spreading in every di- 



* Revue Botanique, 1845, p. 161. 

 t Martius, Die Kartoffel-Epidemie, Tab. 3, fig. 18, 21. 

 X In the supposed fungous substance he found 9'75 per cent, of azote, while 

 mushrooms from the bed contain 9-78. 



