396 



attack is to be emphasized, because, at times, up to the present, observers 

 have emphasized especially that all the stems on a tuber become diseased, 

 i, e. that the cause of the disease must lie in the whole tuber, while my 

 observations have shown beyond question that the diseased condition may 

 be limited to a few eyes. 



According to Kiihn', the disease appeared as an epidemic first in 1770 

 in England and in 1776 in Germany, causing extraordinary losses. The 

 first symptom is the discoloration of the leaves which no longer have the 

 fresh appearance of healthy plants. The main leaf stem is usually found 

 bent downward or completely rolled up; the various leaflets are folded, 

 curled here and there and covered with brown, usually longish spots. The 

 latter extend as far as the main rib of the leaf and finally to the stem. At 

 first only the superficial cells are brown, later the disease extends deeper 

 into the tissue, even to the pith of the stem. This changes the consistency 

 of the stem from a normal flexibility to a glassy brittleness. In addition, ' 

 according to Schacht, sugar is found very abundantly in the diseased cells-. 

 If such plants live until harvest time, they either set no tubers at all or only 

 a very few. 



In the earlier literature, very different causes (including parasitic 

 fungi) are given, as shown by reference to the previous edition of this 

 manual. Newer theories may be found in Frank's^ study. He distinguishes 

 a number of different forms of the disease and, agreeing with me, states 

 that the very beginnings of the diseased condition do not show any fungous 

 action. The cause of the death of the protoplasm in the various brown 

 tissue centers is not known. Differing from my observations, however, 

 Frank emphasizes "that all the shoots of a plant became sick simul- 

 taneously*." 



In making more extensive cultural experiments, using several varieties, 

 and directed especially to the study of leaf curl, I found that the phenom- 

 ena of disease appeared initially only in one variety (Early Puritan). The 

 diseased plants, scattered among the healthy ones, made only a third as 

 much growth and showed the well-known characteristics, especially the 

 breaking of the curled leaves. Small corky fissures were often found on the 

 petioles. The first stages of the disease on the stems were found in one of 

 the internodes below the surface of the soil, where a blackening of the duct 

 walls could be determined. This characteristic can be traced back, radiating 

 more or less deeply into the tuber which otherwise seems healthy. This 

 shows that the tuber has not carried the disease to the shoot but, conversely. 

 In the same wav, the browning of the ducts radiates out from the diseased 



1 Kiihn, Jul., Krankheiten d. Kulturgewachse. 1858, p. 200. — Ber. aus. d. 

 physiolog. Laborat. d. landwirtsch. Institufs zu Halle. 1872, Part 1, p. 90. 



2 Bericht an das Kgl. L.andesi3konomiekollegium liber die Kartoffelpflanze und 

 und deren Krankheiten. 1854, p. 11. 



3 Frank, A. B., Die pilzparasitiiren Krankheiten der Pflanzen. Breslau 1896, 

 p. 300. — Kampfbuch gegen die Schadllnge unserer Feldfriichte. Berlin, Parey, 

 1897, p. 217. 



4 Kampfbuch p, 222. 



