52 



DISEASES OF CROPS. 



22) is examined beneath the microscope,^ the mycelium of 

 the fungus will be seen ramifying among the cells of the 

 leaf. "Wherever the mycelium comes in contact with the 

 cells of the host-plant, they become discoloured. This is 



Fig. 22.^PoTATO FcNans {Peronospora infestans). 



A to B. Transverse section of potato leaf, showing mycelium (spawn) of fungup. 

 A. Lower surface with two stomata (C) and conidiophores passing tiirough 

 them. 



D. Conidium (spore). 



E. Zoospore. 



F. Odgonium and antheridinm. 



6. Pallisade parenchyma cells of leaf. 

 H. Spongy parenchyma. 



( X 100 diam.) 



due to the putrefactive changes caused by the presence of 

 this fungoid growth. The mycelium gives rise to aerial 

 hyphee (conidiophores) which bear conidia or spores (Fig. 



* In our opinion, the best "objectives" for this and similar pur- 

 poses are those made by Zeiss of Jena. 



