182 



oeton: pathology of solanum tuberosum 



as cool as in Chili, though the rainfall is less (figs. 1 and 2). Nor- 

 thern Germany is justly renowned for its potato harvests, which, 

 in bushels per acre, are more than double those of the United 

 States, and there also the growing period is long, cool and equable. 

 The limiting factor is the rainfall, which is low, tho well distri- 

 buted (Cf. Edinburg and Posen in figs. 1 and 2). 



The July isotherm of 65°F. crosses North America not far from 

 the northern border of the United States. Only in Aroostook 

 County, Maine, and parts of northern New York have we develo- 

 oped extensive potato culture north of this isotherm, which in 



Fig. 1. Curves of mean monthly temperatures for Valdivia and Puerto Montt, 

 in southern Chile, compared with Edinburgh, Scotland; Posen, Germany; Hand, 

 cock, Wisconsin; Aroostock County, Maine; Federal Point, Florida, and Washing- 

 ton, D. C. Data from the firgt four were compiled from Hann's "Klimato- 

 graphie;" the latter four from reports of the U. S. Weather Bureau. 



Europe runs south of the principal potato districts of Great Britain 

 and northern Germany. The isotherm of 70°F. (21°C.) for June, 

 July and August nearly marks the southern boundary of successful 

 main crop potato production in the United States. The climate 

 of the greater part of the United States is therefore too hot for 

 best results with this crop. As shown in figures 1 and 3, the pro- 

 duction of potatoes in the South is a matter of early spring plant- 

 ing and summer harvesting, or of planting in late summer for 

 autumn harvests. For the latter procedure a type of potato illus- 

 trated by the variety McCormick is well adapted in the region of 

 Washington, D. C, a fact worthy of mention here for its signifi- 

 cance in the problem of securing a heat resistant potato for south- 

 ern districts. The summer heat of the United States is the limit- 



