52 



DISEASES OF CROPS. 



22) is examined beneath the microscope,i t^g 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 FnNous (Peronospora infestans). 



A to B. Transverse section of potato leaf, showing my celiom (spawn) of fungnp. 

 A. Lower surface Witt two stomata (C) and eonidiophores passing through 

 them. 



D. Conidium (spore). 



E. Zoospore. 



F. Oogonium and antheridium. 



G. Fallisade parenchyma cells of leaf. 

 H. Spongy parenchyma, 



(x lOOdiam.) 



due to the putrefactive changes caused by the presence of 

 this fungoid growth. The mycelium gives rise to aerial 

 hyphse (eonidiophores) 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. 



