28 



DISEASES OF CROPS. 



the larva of this insect causes considerable damage to the 

 crops of Russia. 



Prevention. — As the caterpillars feed upon nettles and 

 low-growing grasses, these should be cleared away. 



Cure. — A good dusting with lime or soot is a sure 

 remedy for this pest. 



The Pea Mildew {Erysiphe Martii, Fig. 9) is very 

 destructive, as it " grows on both sides of the leaves," 

 causing white spots. The spores of this fungus throw out 



>.zoo. 



Fig. 9.— Pea Mildew (Erysiphe Martii). 



A. Oidium stage of the Pea Mildew, showing mycelium and spores. 



B. Conceptacle, or the perfect stage of the mildew, 



C. Section of the conceptacle, showing ascl containing spores. 



D. An ascuB with spores. 



hyphse, which are provided with suckers. These suckers 

 (haustoria) pierce the epidermis of the host-plant, and 

 thereby impede its growth. The hyphse soon produce a 

 mat-like mycelium within the leaves of the pea-plant. 

 During the early summer the mycelia give rise to a num- 

 ber of vertical groups of conidia or spores (Fig. 9 A). 



