Mr. Crum on the Potato Disease. 93 



there, as in most other cases of decay, these plants have no share in pro- 

 ducing disease in vegetables, but are a necessary consequence of the pro- 

 duction of putrid matter — a soil in which alone they can vegetate. I 

 made known these experiments as extensively as possible, for at that time 

 some countenance had been given td the opposite opinion, that the seeds 

 of fungi do fix themselves upon, and produce disease in otherwise healthy 

 plants ; and some apprehensions were consequently entertained, particu- 

 larly in Ireland, that danger might result even to grain crops sown upon 

 land which had grown diseased potatoes, from the prevalence in it of the 

 seeds of these fungi. 



I related at the same time an experiment which led me to doubt the 

 statement of Professor Kutzing, (although the wetness of the season 

 appeared to confirm it), that the rupture of the cells was occasioned by 

 their containing a more than ordinary quantity of water. All facts on 

 such a subject are important, and as these views are still held by some 

 who have adopted the general statements contained in my first paper, I 

 shall relate some recent experiments which satisfy me that diseased pota- 

 toes contain no more water than healthy ones. 



I had no means of comparing satisfactorily the potatoes of this with 

 those of other years; but I experimented upon various kinds, some of 

 them as sound as the potatoes of any previous year. The potatoes, after 

 being wiped dry were carefully sliced into pieces of about two lines in 

 thickness, and two middle slices from different specimens were employed 

 in each experiment. The drying was performed at a steam heat, and 

 was continued nearly three days, when they had ceased for some hours to 

 lose weight. 



Specimens 1, 2, 3, and 4, in the table which follows, were potatoes 

 from the same field. 1 and 2 had been pitted a month. 3 and 4 had 

 been left in the ground, and were kept moist till operated upon. 1 and 

 3 were perfectly sound and excellent potatoes. 2 and 4 were diseased. 



5 and 6 were sound potatoes grown on wet bog land, and pitted a 

 month in a damp situation. 7 was the same, diseased. 



8 and 9 were potatoes of different sorts ; both perfectly sound, as was 

 the whole of the crop in the two fields from which they were taken. 

 8 was a mealy good potato ; 9 was a waxy potato, not well tasted. 



10 was a rough red potato and quite sound — dug end of August before 

 the disease had appeared in this country. 11 the same, left accidentally 

 in the ground till December, and also quite sound. 12, forty-fold potato, 

 left in the same manner in the ground, and quite sound. 



If a potato bo cut into slices, and one of the middle pieces be held up to 

 the light, it will be seen that the outside, all round, is denser than the 

 centre. A distinct boundary (a narrow space containing the spiral ves- 

 sels) divides the two portions, which, in a middle slice, are nearly of equal 

 weight. It is in the external denser portion that the disease appears — 

 nuimiencing at the surface and proceeding inwards. The boundary I 

 have mentioned often arrests its progress. The following table shows the 



