THE FUNGI WHICH CAUSE PLANT DISEASE 



653 



oxy- 



(see p. 46) of potatoes; it is perhaps identical with F. 

 sporum. 



F. erubescens A. & v. Ov. produces small black sunken spots 

 on green and ripe toma- 

 toes in Germany *'"' re- 

 sulting finally in mummi- 

 fication. Parasitism by 

 means of enzymes was 

 demonstrated. 

 F. lycopersici Sacc.^"'"^"- 

 Sporodochia as in F. oxy- 

 sporum; conidia falcate, 



acute, 25-30 x 3.5-4 fi, .^^SS^S^SZSS^KSU H-i 



hyaline to yellowish. 



It is the cause of a to- 

 mato wilt or "sleeping 

 disease" resulting from in- ^'°- ^*^-^- "'^- ^*"" ^°""y- 



vasion of the ducts. Conidia of two kinds are produced, Fusa- 

 rium and Diplocladium. Infection is subterranean. 



A nearly related disease differing chiefly in the fact that the 

 fungus does not reach far above ground has been described by 

 Smith.^"^ The fungus in both cases is perhaps identical with 



F. oxysporum. 

 F.liniBoll.«' 

 Sporodochia erum- 

 pent, compact, cream 

 to flesh-colored; co- 

 nidiophores short, 

 much-branched; co- 

 nidia 3-septate, fusi- 

 form, slightly curved 

 to falcate, 27-38 x 

 3-3.5 li. 



A serious widespread flax wilt is caused. The mycelium develops 

 luxuriantly from bits of diseased stem laid in sterile Petri dishes 

 and grows well in culture media. Normally a soil saprophyte, it 

 invades the roots, grows through the veins, plugs the ducts and 

 causes death. The sporodochia are found abundantly on the bases 



Fig. 444. — F. lini, sketch, showing the mode of attack 

 upon a young root tip of a seedling flax plant. 

 After BoUey. 



