THE MODERN POTATO PROBLEM 239 



ern potato problem. Entomologists have recently dem- 

 onstrated an apparent close association of the insects 

 known as leaf-hoppers with tip-burn and they have been 

 inclined to carry this condition over into their domain 

 and have renamed it hopper-burn. It has also been 

 claimed that the secret of tip-burn on the potato foliage 

 is to be found in the water pores, or hydathodes, which 

 are grouped around the margin of the leaf on the upper 

 side and masked toward its tip end. The death of the 

 marginal vein is due to the loss of water from these 

 pores which lie over it. This is followed by a browning 

 of the entire region. Attention is particularly called 

 to the fact that the plant can control the opening and 

 closing of the stomata but that the hydathodes remain 

 open permanently. 



Modern potato disease research in common with re- 

 search on plant diseases in general has assumed a much 

 broader scope than formerly. In the past the pathol- 

 ogists devoted most of their studies to the parasite. 

 This type of research is now being supplemented by 

 physiological studies. The influence of environment on 

 disease is being emphasized. Investigations are yield- 

 ing results of tremendous practical importance. They 

 are explaining the variability in the occurrence of cer- 

 tain diseases both in general and local areas. The 

 factors influencing the susceptibility of the plant to 

 various diseases and the physiological responses of the 

 plant to the invading organisms are problems awaiting 

 further research. 



POTATO STORAGE. The storage and transportation 

 of plant food products is becoming a national problem, 



