196 



DISEASES OF CULTIVATED PLANTS 



the leaf-stalks. Its presence is indicated by the white patches 

 bordered with orange-red. The fungus passes from the leaf- 

 stalks into the root, penetrating to the heart, causing a rot. 

 The conidial fruit first appears on the leaf-stalks, followed by 

 the ascigerous form when the leaves are quite dead. 



Ascigerous form. Perithecia rounded, brown, asci oblong- 

 clavate, 8-spored ; spores hyaline, 1 -septate, upper cell ovate- 

 rounded, largest, lower cell narrower, 21 x 7*5 /*. 



FlG. 53. Sphaerella tabifica, causing hcrm-rot of 

 orange-globe mangold. 



Conidial form. Perithecia subglobose, conidia elliptical, 

 hyaline, 5-7 xy$ p, escaping as a gelatinous tendril. 



As the disease appears somewhat late in the season, it is 

 advisable to lift the crop when it is first observed, before the 

 fungus passes from the leaves into the root. Diseased ' tops ' 

 should be collected and buried. It is important not to 

 include diseased roots when storing, and if diseased roots 

 are found when the pits are opened they should not be 

 thrown on the manure heap or into the pig-stye, but buried, 

 otherwise the disease will find its way back to the land. 



Frank, Zeitschr. Zucherr., 1892, p. 904. 



MWeeney, fount. Roy. Agric. Soc, Ser. 3, 6, pt. 3 (1895). 



Prill ieux, Malad. des Plantes Agric, 2, p. 263 (1897). 



