JAMIESON AND WOLLENWEBERI FUSARIUM TRICHOTHECIOIDES 147 



concerning the loss of potatoes in storage that complaint is most 

 frequently heard. 



Potatoes affected with this external dry rot are characterized 

 by wrinkled, discolored, and somewhat sunken external spots, 

 frequently but not always occurring at the "eye" end of the tuber, 

 and varying in diameter from a few centimeters to several inches 

 according to the progress of the disease. The color of these dis- 

 eased areas is in general brownish, considerably darker than that 

 of the normal epidermis and often having a slightly grayish cast. 

 In a more advanced stage of the disease the epidermal tissue often 

 breaks or cracks irregularly, exposing a substratum of fungus 

 mycelium within. The surface of the tuber about the cracks 

 may also be overgrown with a delicate pinkish-white, powdery 

 growth, composed of fungus threads and spores. From sections 

 made thru diseased tubers, the internal fleshy portion is seen to be 

 seriously affected, often to a greater extent than is apparent from 

 the external appearance. The internal discoloration is sepia 

 brown, a cross section of a badly diseased potato often showing a 

 pronounced contrast of shades varying from light to deep brown. 

 As infection proceeds internal cavities are formed, from one to 

 several centimeters in diameter, within which the fungus mycelium 

 grows abundantly, presenting the same powdery appearance as 

 noticed on the surface of the tuber. Gradually the whole sub- 

 stance of the potato becomes involved, until finally it is reduced 

 to a dry, powdery, brownish-colored mass of broken-down cells, 

 starch grains, fungus mycelium and spores. Tissue from various 

 parts of infected tubers showed a fungus belonging to the genus 

 Fusarium thruout the discolored portions as well as in the firmer 

 tissue bordering upon these areas. A pure culture of this Fusa- 

 rium was isolated from the inner tissue by the agar plate method. 

 During our further investigations the same fungus has been iso- 

 lated several times from dry-rot infected potatoes. 



The following description and diagnosis of this Fusarium is 

 now being added in the monograph of Dr. Wollenweber: 



Fusarium trichothecioides Wollenw. In general appearance 

 this fungus closely resembles Trichothecium roseum (Link) ; Conidia 

 in nature as a rule not in sporodochia, but, in pure culture the 



