No. 7. 



Disease in the Potatoe. 



213 



Silesia and Meklenburg, and continued in- 

 creasing in intensity, and spreading more 

 and more, until it reached its height in 

 1840. 



The rot may be designated by the dry and 

 the moist rot, according to the degree of 

 moisture either contained in the tuber, or 

 acting from without, upon it. Symptoms of 

 this disease are : the potatoes brought home 

 to the cellar, and the seed potatoes when 

 laid ort the field get rapidly rotten, and the 

 latter either rot before the leaves have 

 sprouted, or they produce but small and 

 scanty lateral tubers, closely attached to the 

 seed potatoes, of the size of musket-bullets, 

 which produce but very slender stems; or 

 the plants that are grown from them, are 

 but meagre and soon droop and wither. At 

 any rate, but few small and weak tubers are 

 produced. These, when but little exposed 

 to moisture, appear dry and hard, of a con- 

 sistency like that of truffles, and unable to 

 produce any eyes; when brought into the 

 ground, they soon rot by attracting the 

 moisture from the ground. Fields that 

 sutler much from this disease, look like 

 stubble fields, where potatoes, left here and 

 there from last harvest, have sprouted. The 

 flowers show themselves very unequally on 

 such plants, and but very seldom produce 

 fruit. 



The rot seems to have appeared princi- 

 pally in those parts of Germany, where a 

 denser and more industrious population cul- 

 tivate the potatoe in a more rational, but 

 also more refined way, and chiefly where 

 they raise their potatoes, not by laying whole 

 tubers, but by cutting these into several 

 slices. 



Too great economy in planting the pota- 

 toe, seems therefore, to have an essential 

 influence on producing this epidemical dis- 

 ease. The two forms of mushrooms that 

 are observed most frequently in potatoes at- 

 tacked by the rot, are set by Martins under 

 the genus Fusisporitwi, and are called by 

 him, Fsp. Solani, and Fsp. sporolrichoides. 



Chemical analysis. — Dr. Andr. Buchner, 

 jr., found on a chemical analysis of potatoes 

 infected with the rot, which he made at the 

 request of Dr. Martius, that no new sub- 

 stance had been formed in them ; they con- 

 tained a considerable quantity of amylum 

 in cases where the moist rot had not shown 

 itself, but only the dry one — and its quality 

 was not altered; but the albumen Iiad disap- 

 peared entirely, and the quantity of water, 

 of which the sound potatoes contained 73.6 

 per cent., had been reduced in the diseased 

 ones to less than the half, i. e., to 85.6 per 

 cent. The fibrin in them was of a brownish 

 colour, and in part already mouldy. 



Scab. — There appears often at the same 

 time with the rot, another disease less inju- 

 rious, called the Scab, which occurs, how- 

 ever, also sporadically, from a great variety 

 of external causes. As far as it is known 

 to Martius, the scab produces but very rarely 

 an entire alteration of the substance of the 

 seed potatoes. It is distinguished from the 

 rot, by its being merely a corruption of the 

 cellular tissue, that lies immediately under 

 the epidermis, followed by the generation of 

 a mushroom, called by him, Prolomyces tu- 

 beritm Solani — and by the destruction of the 

 epidermis. The rot on the contrary, infects 

 the entire substance of the potatoe, and is 

 an induration and a mouldiness of the tuber. 



Sometimes also the tubers that are at- 

 tacked by the scab, pass into a state of pu- 

 trefaction, or produce but feeble stems, with 

 fewer tubers, yet far less frequently than 

 those attacked by the rot. Dr. Martius has 

 not been able to determine, whether the scab 

 and the rot occur together on one and the 

 same field, or even on one and the same 

 plant. 



Causes of the rot. — There are both exter- 

 nal and internal causes of the rot, of which 

 the former regard, first, the preparation of 

 the seed potatoes for laying, and the soil, 

 wherein to plant them ; second, the state of 

 the weather; and third, insects wounding 

 the plants. The internal or predisposing 

 causes regard first, the peculiarities of the 

 different sorts of potatoes; second, the man- 

 ner of treating the plant on the field, and of 

 treating the seed potatoes from harvest time 

 to the time of planting them; and third, the 

 way of laying the tubers, and of treating 

 the plant till its maturity. 



Soil. — The chemical composition and the 

 degree of density of the soil, seem to have 

 the greatest influence on the growth of the 

 potatoe. In its native country, in Peru and 

 Chili, it grows in cold mountain regions and 

 in a stony soil that is rich in loam, but suffi- 

 ciently loose. In Europe the sandy soil has 

 been found the most convenient. The rot 

 has been observed, however, on all kinds of 

 soil, comparatively speaking; however, less 

 frequently on a light, sandy, loose soil, rich 

 in mould, than on a hard and heavy one. 

 The scab of the potatoe, on the other hand, 

 has been observed principally on lime soil. 

 It is not so much, however, the original 

 quality of the soil, as the particular way of 

 preparing it, which seems to influence the 

 rot, since it has been observed even on fields 

 that were manured carefully, at the right 

 time and with old dung, whilst other fields 

 badly cultivated, or not manured at all, re- 

 mained free from it and yielded even good 

 crops. 



