ON POTATO " LEAF BLOTCH " AND " LEAF CURL." 621 



stem and leaves bear numerous blackish-olive, minutely velvety patches 

 of various forms and sizes." He further states that when a potato plant 

 is badly infected the mycelium of the fungus passes from the haulm 

 into the underground branches and young tubers. 



According to Massee, therefore, and in the particular case described 

 by him, a parasitic fungus is present in the tissues of the tuber used 

 for planting; as the plant develops the fungus passes by means of the 

 conducting tissue from the " set " into the young haulm and even- 

 tually reaches the leaves. Whilst this is going on the mycelium passes 

 from the haulm into the underground branches and young tubers. 



With regard to the ' President, ' a sequence of events similar to 

 that described by Massee has not yet been observed. In the instances 

 examined, the disease did not pass hy means of the conducting tissue 

 from the " set " into the haulm and leaves, nor did it pass from the 

 haulm into the young tubers. The disease, on the other hand, worked 

 its way from the surface of the leaves into the more deeply seated 

 tissue. It seems very likely that the fungus or fungi associated with 

 this disease exist on the skin of the potato, and partly owing to the 

 elongation of growing organs, are carried, externally, during growth, 

 to the various parts of the plant. 



In 1906, L. E. Jones and C. S. Pomeroy* described a leaf blotch 

 disease of potato, prevalent in some parts of the United States. This 

 disease is said to be due to the fungus Gercospora concors. 



From the published accounts it would appear that a blotched condi- 

 tion of the potato leaf may be brought about by more than one fungus, 

 and perhaps by different combinations of fungi. 



. The leaves of the potato may be folded, crinkled, rolled or curled 

 in various ways, when they are not otherwise disfigured. This has been 

 recorded recently by Masseef (1910), 0. Appel^ (1908), Schleh§ 

 (1909), and Steghch|| (1909), in Germany; Ducloux and mdiardf 

 (1909), in France, and numerous other investigators. 



During the course of some experimental work in the North of 

 England, in connexion with a local epidemic of Phytophthora infestans, 

 de Bary, carried out in 1909, a number of plants with rolled or curled 

 leaves were noticed in a twenty-acre field owned by George Pol- 

 lard, Esq., of Cleadon Grange in the County of Durham. Accordingly, 

 over one hundred plants were specially marked so that they could be 

 recognized at the time of lifting the crop. These were dug up 

 separately, and it was found that they were almost invariably affected 

 with Blackleg, which is the British equivalent of a disease described 

 by Erwin Smith** (1896) as A bacterial disease of the tomato, egg 

 plant and Irish potato," and of that described by Grotenfeldfj (1901), 



* L. K. Jones and C. S. Pomeroy. Vermont Sta. Report (1906), pp. 236-57. 

 t Massee. L.c. p. 501. 



X 0. Appel. Jahresher. ver. Angew. BoL, 6 (1908), pp. 259-65. 



§ Schleh. Fuhling.^ Landw. Ztg. 58 (1909), No. 18, pp. 641-63. 



II Steglich. Sachs Landw. Ztschr, 57 (1907), No. 17, pp. 296-98. 



H Ducloux and Hediard. Betterave, 19 (1909), No. 487, pp. 299-300. 



** Erwin Smith. U.S.A. Dey. Agr., Bull. 12 (1896). 



ft Grotenfeld. Hufondstodshladets Landthrukshilagen (1901), No. 5. 



