POTATO WILT, LEAF-BOLL, AND RELATED DISEASES. 27 
the leaves, and normal color and turgidity. This is further described and illustrated 
on page 37. 
(e) Wilt of both the Fusarium 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 lsaf-rol 7 
plants live nearly as long as healthy ones. 
(J) 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 "Krauselkrankheit," 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 Kreitz, 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 margins of the leaflets due 
to excessive transpiration during hot, dry weather. Tip-burn is com- 
paratively much less prevalent in the cooler climate of Em-ope than 
in the United States, but it was observed by the writer in typical 
form in Dresden during the hot, dry summer of 1911. 
LEAF-ROLL IN EUROPE. 
The leaf-roll disease of potatoes first came into public 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 many 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 published: (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 fur Land- und Forstwirtschaft at Dahlem, Berlin, 
