138 



THE FUNGI WHICH CAUSE PLANT DISEASE 



walled and short livfed, the later ones thicker walled and more 

 enduring. 



After some weeks these tufts cease forming and disappear. The 

 mycelium within the fruit persists, turns olivaceous and forms 

 large irregular sclerotioid masses which on the following spring 

 may produce fresh conidia. 



These sclerotioid (mummified) fruits under suitable conditions 



Fig. 92.-|-Sclerotinia on plum, o, section showing a spore pustule and chains 

 of conidia; 6, part of a spore-chain; c, spores germinating; d, a mummy 

 plum and ascophores; e, an ascophore; /, ascus; g, mature spores. After 

 Longyear. 



in nature, usually at blossom time of the host, can also produce 

 apothecia, a fact first demonstrated by Norton. ^^ 



These apothecia develop in large numbers from old fruits half 

 buried in soil, and send forth ascospores to aid in infection. The 

 ascospores germinate readily in water and it was proved by Norton 

 that they give rise to a mycelium which produces the characteristic 

 Monilia. Inoculation of ascospores on fruit and leaves also gave 

 positive results in two or three days. The flowers, and through 

 them the twigs, are also invaded by the myceliimi which seeks 

 chiefly the cambium and bast. Shot-hole effect is produced on 

 leaves of peach and cherry (Whetzel ^'). Infection is frequently 

 through minute wounds.** 



