PLUM LEAF BLISTER 



135 



PLUM LEAF BLISTER 



(Polystigma rubrum, Pers.) 



A parasite often proves injurious to plum and almond 

 trees by destroying the foliage. It also attacks the sloe and 

 white-thorn. Reddish patches appear on the leaf, most 

 frequently, but not always, on the lower surface; these 





Fig. 25. Polystigma rubrum. i, diseased plum 

 leaves ; 2, section through a stroma, showing the peri- 

 thecia ; 3, asci containing eight spores, produced in a 

 perithecium, X3oo; 4, spermatia, produced in spermo- 

 gonia, x 300. 



spots soon develop into thickened, cushion-like stromata, 

 the surface of which, towards the end of June, becomes 

 thickly studded with minute darker dots, which correspond 

 to the mouths or openings of flask-shaped receptacles 

 imbedded in the stroma, called spermogonia. These 

 structures contain numerous slender, curved bodies, called 



