426 



growing regions of the world* except the irrigated districts ot the western 

 part of the United States, which are shown by the extension of this large area 

 by dotted lines at the left. The inner area (enclosed by the dot-dash line) 

 in each part of the figure indicates the limits of average data for European 

 countries alone, which may be considered as the most favorable conditions 

 because extremes of temperature and rainfall are thus excluded. The Sophia 

 data fall generally within these medial conditions; while the data for the 

 other two localities, which are at a higher altitude, do not. It is probnble 

 that a complete analysis ot the climatic relations of the apple and the codling 

 moth would help to settle the question of the origin of the moth. On the 

 hypothesis that this origin was in the territory around the eastern Mediterran- 

 ean, where conditions fall witliin the small area shown in Fig. 31, the difference 

 between a "scarce" and an "abundant" year in Illinois is explicable. Since the 

 hythergraph for southern Illinois does not always fall entirely within this 

 area of favorable conditions, both winter and summer temperatures sometimes 

 reaching extremes, the codling moth is abundant here only in years when 

 these general limits are not exceeded. At least, the important effects of autumn 

 and winter rainfall, as pointed out in this paper, suggest the Mediterranean 

 region as the original habitat of the codling moth. 



(E) EXPERIMENTAL METHODS. 



In the experiments reported in this paper many important innova- 

 tions were employed, especially in the controlling and recording of vari- 

 able conditions of temperature, humidity, air movement, and evaporation. 

 Most experimental work has formerly been done with constant tempera- 

 tures. We know of no other attempts to use variable temperatures of an 

 interpretable type, with factoi"S all recorded, as a means of bridging the 

 gap between constant-temperature experiments and acttial weather condi- 

 tions. The chambers for constant-temperature work are unique in that 

 they allow the use of several humidities at the same temperature. This 

 feature is essential, because variation in stock necessitates the running of 

 a large series started at the same time from the same stock. This is a 

 very important feature for climate-simulation work. 



A. General Equipment. 



1. Building. This Vi'ork was done in the Vivarium of the Univer- 

 sity of Illinois. The greater part of the work was carried on in a glass- 

 roofed house of greenhotise construction. The room was provided with 

 center-roof and side ventilators, and a door at the end. To facilitate air 

 circulation, three fans were placed on the bottom of the side ventilator 

 on the south. The room was heated by steam radiators regulated by a 

 Johnson automatic temperature control, as described by Harding and 

 Willard ('16). 



2. Apparatu^s. The constant-temperature experiments were con- 

 ducted with the apparatus regularly used in the Vivarium, which will be 



* The following countries were included in tliis category: Great Britain, Spain, 

 France, Germany, Denmark. Au.stralia, Tasmania, Canada, and the United Slates. 



