128 DISEASES OF CROPS. 



manure, without losing their vitality {Chemical News, 

 vol. 49, p. 279). 



Cure. — (1) Lands whicli Lave grown infested crops 

 should be treated with quicklime or gas-lime. (2) A top- 

 dressing of iron sulphate (|- to 1 cwt. per acre) in the 

 spring destroys the early stage of P. rubigo-vera. 



The Summer Rust of Corn (Puccinia graminis, 

 Kg. 45). The Uredo, or early stage, of this fungus makes 

 its appearance in the summer, usually about July. Un- 

 like the " spring rust," the " summer rust " produces 

 pallid spots (sori) on the leaves and culms of com and 

 grass plants. The early or rust stage is known as Uredo 

 linearis (the specific name referring to the elongated 

 form of the sori) ; and the second or mildew stage as 

 Puccinia graminis. The sori of the mildew stage are 

 black, and make their appearance in the autumn and 

 winter. The sori of the rust stage of this fungus are not 

 unlike those of Puccinia coronata (see Fig. 37 A and B). 

 If a transverse section of a small rust sorus is examined 

 under the microscope, a mass of oval-shaped spores will 

 be observed, supported on hyphss rising from a closely- 

 packed mycelium which infests the host-plant (Kg. 45 A). 

 These spores (uredospores) rupture the epidermis of the 

 host-plant, and thereby greatly interfere with its life- 

 history. In fact, the fungus causes disease, by obtaining 

 nourishment from the protoplasm and sap of the living 

 cells of the infested plant, as well as causing no incon- 

 siderable amount of damage by rupturing the epidermis. 

 After liberation, the uredospores may fall on the leaves of 

 wheat and other cereals, where they germinate by giving 

 rise to hyphse which pass into the interior of the host- 

 plant through the stomata. The hyphee reproduce the 

 uredo-mycelium with its accompanying spores. During 



