NECTRIA 183 



The fact that the Nectria or ascigerous condition is only 

 formed on the old dead skin of the potato the season follow- 

 ing the appearance of the conidial condition, perhaps 

 accounts for its not being previously connected with the 

 disease. 



Ascigerous form. Perithecia crowded on a stroma, minute, 

 conic-globose, smooth, blood-red, asci clavate, 8-spored ; 

 spores elliptical, hyaline, i-septate, slightly constricted at the 

 septum, 8-9x5 fi ; paraphyses slender, tips strongly clavate. 



Monosporium stage. Conidiophores usually with pairs of 

 branches at different levels, branches bearing opposite 

 branchlets, each terminated by a minute, globose, hyaline 

 conidium 4-6 /j. diam. 



Fusarium stage. Conidiophores elongated, simple or 

 branched, conidia hyaline, fusiform, arcuate, 3-5-septate, 

 15-40 X 5-8 ji, but size very inconstant and variable. 



Cephalosporium stage. Conidiophores short, simple, spring- 

 ing as lateral branches from creeping hyphae that often run 

 in parallel fascicles or strands, conidia produced in a cluster 

 at the tip of the conidiophore, where they become free, but 

 are fixed at the apex of the conidiophore for some time in a 

 globular mass of mucilage, resembling the head of a Mucor, 

 conidia Fusarium-shaped, hyaline, becoming septate, 6-12 X 



3-4 !* 



The tubers are probably infected while growing, but some- 

 times there is no sign of disease when they are lifted. If 

 thoroughly dried before storing no further development takes 

 place, whereas if sweating occurs after storing, the disease 

 spreads rapidly. When storing, powdered sulphur at the 

 rate of about 2 lb. to the ton should be sprinkled over the 

 potatoes. This checks the development of the fungus, and 

 also destroys mites, etc., that convey the spores from one 

 potato to another, where infection takes place through 

 wounds. 



Land that has produced a diseased crop is certain to be 

 infected, and should be dressed with kainit or lime. 



Board of Agric. Leaflet, No. 193. 



Apple-tree canker. This well-known disease is caused by 

 Nectria ditissima (Tul.), which by no means confines its 

 attacks to this tree, but is equally common on beech, oak, 

 hazel, ash, hornbeam, maple, lime, dogwood and bird-cherry. 



