PLATE IV 

 Phytophthora infestans: Infection of potato tubers 



Fig. I . — Cross section of a tuber which was infected with P. infestans and was planted 

 in the greenhouse in rather drj^ soil. After two months it was dug up and found to 

 be j5rm and containing living mycelium of the fungus. 



Fig. 2. — This tuber was inoculated at the eye surrounded by the paraflfin ring. The 

 mycelium ran through the tissues and grew out into four of the sprouts at the bud end of 

 the tuber. 



Fig. 3. — Cross section of an infected tuber planted in sterilized soil in the green- 

 house which developed a shoot that became infected through the parent tuber. 



Fig. 4. — The small stunted shoot which grew from this infected tuber shows the "pro- 

 gressive discoloration caused by P. i7ifesta-ns growing up the stem. 



