17 



Morphological Development of Erysiphe. 



A cereal leaf affected by the mildew shows velvety spots of an ashy 

 color at first and brown later; elliptical in outline; irregular; from two to 

 three lines long and one to one and a half wide ; more common but smaller 

 on the upper surface, and occupying without preference any place on the 

 entire surface of the leaf. These spots are quite insignificant on the leaf 

 sheath (Fig. 1). 



Under the objective of the microscope these velvety spots take on the 

 appearance of a colourless mass of tangled threads, the whole forming a 

 downy cushion, becoming brown later. Under a stronger magnification 



Fig. 1— Erysiphe graminis. 

 Appearance of Summer Mycelium 

 tufts on a leaf. 



Fig. 2— Erysiphe graminis. 



Fifture A shows a thread of the Mycelium with a sucker or haustorium; 



Figure B show the germination of a summer spore on a leaf. 



Fig. 8— Conidium form ol 

 Erysiphe graminis. 



I. P.— 2 



Fig. 4 — Perithecium of Erysiphe graminis. 



