orton: pathology of solanum tuberosum 181 



De Condolle, after a critical study of the evidence, concludes that 

 the potato is native in southern Chih and expresses doubt as to 

 Peru and the other northern Andean countries, where it was in 

 general cultivation by the natives at the time of the discovery 

 and conquest by the Spaniards and where its present occurrence 

 in a wild or semi-wild condition may be thru escape from the 

 primitive Indian cultures. 



That our potato may have come from a region where high 

 altitudes give a temperate climate within the tropics is, however, 

 not impossible, since other species of Solanum do occur thruout 

 the Andean region and northward as far as Colorado, and may 

 have given origin or contributed thru crossing to the potato which 

 we cultivate today. There is great need for further taxonomic 

 studies to throw light on this point. From the physiological 

 standpoint, however, there can be no doubt that the potato 

 originated in a region of low and uniform summer temperature, 

 a fact of the greatest significance to agriculture in the United 

 States, where different climatic conditions prevail. 



It will be shown that in the Northern Hemisphere those regions 

 are most successful in the cultivation of the potato where the 

 temperatures during the growing period most nearly approach 

 those of southern Chili, and that the climatic environment is the 

 most important factor influencing the diseases of this crop. 



The climate in the district where we believe the potato to be 

 indigenous is marked by very uniformly cool summers and heavy 

 winter rainfall. Valdivia has a meaii annual temperature of 

 52 . 8°F. the maximum is 90°; and the minimum 30° (figs. 1 and 2) ; 

 Puerto Montt and Ancud are similar. To the northward, as the 

 climate becomes hotter and drier, the potato is more and more 

 resstricted to the higher elevations, where the climate is temperate 

 and the summers cool and equable. The relative atmospheric 

 humidity will be high in these cool regions. This is doubtless a 

 more important point for the normal development of the potato 

 than the absolute rainfall. 



Of all countries where it has been introduced the potato per- 

 haps yields best in Scotland, and here we find the summer nearly 



