OBSTRUCTIONS TO DEVELOPMENT 



1 1 , 



age. Near woodland, where the air drainage is poor, 

 the disease spreads rapidly on damp or misty days. 

 Land choked with weeds keeps the lower leaves and 

 stalks damp, and more subject to attack. 



F'G. 36 THE GERMINATING TUBE OF A SPORE OF ROT 



{Phytophthora infestans) 



(After Marshall Ward) 



This may enter a plant through a stomata, or breathing pore, as at a, or 

 it may penetrate the cell wall, as at b. The maintenance of a coat of Bor- 

 deaux mixture all over the plant would check the growth of these spores. 



7. Not digging until ten da) r s after the vines die. 



8. Getting potatoes out of the field as soon as dug, 

 and never covering piles of potatoes with spore-laden 

 haulm. 



