Diseases of the Potato 



185 



prevents it from completely carrying on its life processes 

 and producing its fruit naturally. There are many 

 agencies capable of bringing about disease of the potato, 

 some of which are not well understood at present. Disease 

 may be brought about by conditions of soil and climate 

 unfavorable to the 

 plant, by physiologi- 

 cal disturbances within 

 the plant, the direct 

 cause of which is not 

 clear, and by the 

 attacks of parasitic or- 

 ganisms. Troubles re- 

 sulting from the first- 

 named condition may 

 sometimes be reme- 

 died by selecting vari- 

 eties or types of plants 

 better adapted to the 

 climate in which they 

 grow, or by adopting 

 a system of culture that will overcome or obviate the 

 unfavorable condition. The second group of troubles 

 are often heritable, and the only means of avoiding them 

 are through the elimination of tubers from affected 

 vines for planting purposes. The third type of disease, 

 and often the most destructive, is caused by parasitic 

 organisms and may be communicated to healthy plants 

 by the transfer of the parasite or some special portion of 

 its body adapted for the purpose. 



For convenience in discussing them, we may classify 

 parasites of the potato into plant and insect parasites. 

 The plant parasites include fungi, bacteria and slime- 



FiG. 14. Section through a part of a dis- 

 eased potato leaf, showing the spore stalks, 

 with spores attached, extending down 

 through the breathing pores of the leaf. 



