No. 5. 



The Disease in Potatoes. 



156 



The Disease in Potatoes. 



To THE Editor of the N. E. Farmer, — 



Not having- seen any communication ob- 

 jecting to the views I have taken of the 

 cause of the disease in the potatce, and 

 which subsequent examinations have only 

 tended to confirm in my own mind, I re- 

 sumed the investigation of the subject. The 

 results I now ofier to yon for publication. I 

 have first to notice the idea that this disease 

 arises from worms which are found in the 

 decayed potatoe — and remark, 



1st, That the worms are the same which 

 are found in all rotten potatoes, from what- 

 ever cause the decay may arise. 



2nd, The potatoe decays previous to the 

 worms appearing, for the worms are never 

 found in the sound part of the potatoe, eating 

 their way in or depositing their eggs, nor 

 have I ever seen the worms in that part of 

 the potatoe in which the fungus has abeady 

 commenced vegetating : it is only in the 

 most rotten part that the worms exist, after 

 the fungus has caused this decay. 



3rd, Salt instantly kills the worms, as 

 any one may satisfy h'mself, with the assist- 

 ance of the common compound microscope. 



Under the full impression of the existence 

 of the fimgus in the potatoe, two questions 

 present themselves. 



1st, Is the fungus the cause of the decay, 

 or merely a growth on the tuber already 

 diseased from some other cause? — and 



'2nd, When and in what part of the plant 

 the disease originates, and how is it propa- 

 gated and disseminated ? 



The probability is that the fungus is tlie 

 cause of the disease — for the fungus appears 

 on the skin of the potatoe, and can be traced 

 by its gradually dark colour penetrating 

 from the outside by degrees into the sound 

 inside, the outside fungus developing itself 

 first, and producing slime and rottenness, 

 while the inside yet remains firm and sound. 

 If the fungus resulted from the potatoe first 

 becommg rotten, and thus forming favour- 

 able circumstances for its vegetation, then 

 the presumption is that we should occasion- 

 ally, although perhaps rarely, find parts of 

 the potatoe rotten without the fungus, "which 

 I, at least, have never yet seen. I have 

 often seen heaps of rotten potatoes, without 

 ever before observing this peculiar fungus, 

 which, on account of its smell, cannot be 

 mistaken. If this was therefore a disease 

 merely afieoting the rotten potatoe and not 

 the sound one, it would have been long ago 

 and much more often observed. Dr. Wall- 

 roth, an excellent German botanist, who ap- 

 pears to have closely studied tlie fungus 

 family, observes in the Liimeci, (a botanical 



periodica], published in Germany,) vol. 16, 

 tor 1842, that he has ascertained the disease 

 called tliere the potntce scab, or icart — a 

 kind of swelling or tumor, ending in rotten- 

 ness — to be a species of subterranean fun- 

 gus, which he calls Erysibe suhlerranea, 

 and of which he gives a long scientific de- 

 scription. I am not sufficiently versed in 

 this subject, to decide whether this descrip- 

 tion agrees exactly with the disease at pre- 

 sent under discussion, but it appears to me 

 to difl^er in several particulars. 



The second question, as to the origin and 

 propagation of this fungus, is one which 

 presents great difficulties in its solution. 

 These arise partly from the knowledge of 

 the propagation of the fungus family being 

 yet in its infancy, and partly from the v.-ant 

 of means of pursuing the study of this mi- 

 croscopic subject properly. From the almost 

 universal accounts of the tops of the plants 

 having first died down, and thus indicated 

 the disease, it has suggested itself to me, 

 even if this fungus is really a subterranean 

 species, whether it has not been propagated 

 and disseminated by spores floating in the 

 atmosphere and attaching themselves to the 

 slalk of the potatoe, on that vegetating and 

 extending themselves downwards until they 

 reached the point of junction with the tuber, 

 there producing decay, and the death of the 

 upper part of the vegetable, and afterwards 

 disseminating themselves through the tuber. 



A parallel to this probably exists in the 

 vntshromv, a fungus which is naturally pro- 

 duced from horse droppings, when by being 

 kept dry for a considerable time, they have 

 arrived at a favourable state for the dcvel- 

 opement of the spores. These spores have 

 probably attached themselves to the stems of 

 the hay which has been eaten by the horse, 

 have passed through its stomach and re- 

 mained in an inert state, until favourable 

 circumstances have produced their develope- 

 ment in the droppings. 



I regret that I had not commenced this 

 investigation early enough to have examined 

 the stalk and its junction with the tuber, 

 with the microscope, on the first appearance 

 of its drooping, as all the proof now to be 

 expected from experiments, can only be of 

 a negative character: however, here are 

 such results as I have obtained : 



1st. One of these much diseased potatoes 

 was cut in halves; each half was placed on 

 half a sound potatoe, in perfect contact, 

 placed under a bell glass in a damp, dark 

 atmosphere, temperature 57° to 62°. In five 

 days the sound potatoe was not in the slight- 

 est degree contaminated with the fungus or 

 the worms. 



2nd. A whole diseased potatoe, covered 



