THE FUNGI WHICH CAUSE PLANT DISEASE 



33 



ganism, by some regarded as a parasite, though beneficial, and by 

 others regarded as a mutuahstic symbiont will not be discussed 

 here owing to its beneficial character. 



Fig. 20.— Part of sweet-corn stem parasitized by Ps. stewarti. After Smith. 



Ps. savastanoi (E. F. Sm.) Stev. A rod with rounded ends, 

 sohtary or in short chains, 1.2-3 x 0.4-0.8 ju; motile; aerobic; non- 

 sporing; flagella l-several, often 2-i, polar. Standard agar, 

 surface colonies, white, small, circular, smooth 1.5-3 mm. at three 

 days, edge entire; bouillon thinly clouded, precipitate slight, white, 

 no rim or pellicle. On gelatine no liquefaction; colonies white, 

 round, erose, margin pale. 



