POTATO WILT, LEAF-EOLL, AND BELATED DISEASES. 27 



the leaves, and normal color and turgidity. This is further described and illustrated 

 on page 37. 



(e) Wilt of both the Fusariuni and Verticillium types may at certain stages bear a 

 slight outward resemblance to leaf-roll, but they are distinguishable by the occurrence 

 of the causal fungi, by the discoloration of the wood vessels of the lower stem, and by 

 the brown stain in the stem end of the tubers. These wilts cause the rapid death of 

 the plants attacked, or at the least an abnormally early maturity, while Isaf-roll 

 plants live nearly as long as healthy ones. 



(/) Rhizoctonia stem-blight, as it occurs in Colorado and other Western States, may 

 in one stage be easily confused at first sight with leaf -roll. (See under "Rosette," 

 p. 40.) The leaf-roll symptom may, in fact, be induced by stem injuries of various 

 kinds, but the disturbance is fundamentally different from true leaf-roll in that it 

 is not transmissible. Heribert-Nilsson (1913) has described such a leaf-roll, due to 

 hypocotyl injury by an insect, Agrotis segetum. 



In Germany, leaf-roll was formerly included under the collective 

 term ''Kj-auselkrankheit/' which is now being restricted to curly- 

 dwarf. Appel also separates a '^bacterial ring disease," which has 

 not yet been thoroughly worked out, and which can not at present 

 be identified with any American malady. (Appel and KJreitz, 1907.) 

 A new disease, to be described as "streak," also enters to some 

 extent into the complex situation in America. 



There is little likelihood of confusion with tip-burn, as this disease 

 is already so well known. The illustration, Plate XIV, shows the 

 characteristic browning and curling of the margms of the leaflets due 

 to excessive transpiration dming hot, dry weather. Tip-burn is com- 

 paratively much less prevalent in the cooler climate of Europe than 

 in the United States, but it was observed by the writer in typical 

 form in Dresden during the hot, dry summer of 1911. 



LEAP-ROLL IN EUROPE. 



The leaf-roll disease of potatoes first came into pubhc notice in 

 Europe in 1905, when a small epidemic occurred in Westphalia and 

 other points in Germany. Appel found it in the same year in Den- 

 mark. It is his opinion that it had also prevailed ruany years before 

 but had been forgotten or confused with other troubles under the 

 collective term " Krauselkrankheit. " In 1907 a more general out- 

 break occurred in Germany, and much alarm was expressed (Arnim- 

 Schlagenthin, 1908). The disease was reported on all sides. In 

 Austria the Government appointed a special commission to investi- 

 gate the disease. The experiments thus begun are still in progress. 

 Up to date four reports have been pubhshed: (1) Dafert, 1911; (2) 

 Kock and Kornauth, 1911; (3) Reitmair, 1912; (4) Kock and Kor- 

 nauth, 1912. In these the reader will find recorded many data 

 which are only briefly mentioned here. 



Among other investigations begun then or a little later, and in 

 addition to those of Appel and his assistants at the Kaiserliche 

 Biologische Anstalt fiir Land- und Forstwirtschaft at Dahlem, Berlin, 



