425 



Experiments on combinations of temperature and humidity, where 

 the series is limited, should follow the general trend of the weather of the 

 region and of the season to be studied. This plan will save much time 

 and unnecessary experimentation, provided hygro-thermograph records 

 have been kept : otherwise, some means of using vapor-pressure tables 

 will have to be devised. The changes in humidity do not follow the trend 

 shown by air warmed by other means. 



Fig. ;J0 shows complete data for the Ball-Taylor rainfall-temperature 

 charts, or hythergraphs, for "abundant" and "scarce" years at six locali- 

 ties, with the amount of variation. The conclusions from this study have 

 already been expressed in PART TWO, pp. 350-355, where the parts are 

 shown separately in Fig. 3-7. 



Hythergraphs form a basis for interesting speculation as to the original 

 home of the codling moth. The heavy line in Fig. 31 shows the average monthly 

 temperature and rainfall for a typical year in three apple-growing districts 

 in south-eastern Europe. The large area (enclosed by the solid line) in each 

 part of the figure indicates the limits of average data for all the great apple- 



mm Raiufall 



I2S ISO 



Fig. 31. Hythergraphs for apple-growing regions. 



