144 



PLANT DISEASES 



Rhytisma salicinum, F., forms large pitchy-black patches 

 on leaves of goat willow {Salix capreae, L.) and several 

 other species of willow {Salix). 



CLOVER LEAF SPOT 



(Pseudopeziza trifolii, Fckl.) 



A fungus that not unfrequently proves destructive to 

 crops of lucerne {Medicago sativd) and clover {Trifolium). 

 The leaves are attacked, and first show minute blackish 



Fig. 29. — Pseiidopeziza trifolii. i, a clover leaf badly diseased, 

 nat. size; 2, a pustule or fruit of the fungus bursting through 

 the epidermis of the leaf, which is torn into triangular teeth, 

 slightly mag, 13, an ascus containing eight spores, also two 

 paraphyses, X400. 



specks on the upper surface; these increase in size and 

 extend through the substance of the leaf, showing on the 



