[ 795 ] 



77 F- or a temperature lower than 34 F. is unsuitable 

 for its propagation, the temperature most suitable for its 

 propagation being between 50 to 60 F. The tomato 

 and some other solanaceous plants are also subject to the 

 attack of the fungus and it is necessary to suspend the 

 cultivation of all these crops for 2 or 3 years when the 

 potato-rot appears in any locality. 



FIG. 74. PERONOSPORA INFESTANS. 



Explanation of the figure. (a) Section through an infected potato-leaf, 

 showing greater protrusion of the fungus from the under surface than from the 

 upper surface of the leaf (X5o). (b) Conidiophore with conidia shown 

 greatly magnified (X2SO) (c) and (d) Zoospores coming out of a conidiophore. 

 O) Germinating zoospore. (/) Promycelium from zoospore. (g) Promy- 

 celium growing directly out of a conidiophore. (h) and (j) Qogonia and Antheri- 

 dia inside the potato-leaf shown enlarged (X25o). (k) Germinating oospore. 

 (/) Zoospores coming out of an oospore. (m) Germinating zoospore. 



j 065. If a particle of an affected leaf is examined under 

 the microscope it will be seen that the fungus grows chiefly 

 at the lower part of the leaf, and the growth is downwards 

 from leaf to stem and from stem to tuber. The mycelium or 

 spawn-threads will be found branching out and bursting 

 through the stomata of the lower surface, and wherever 



