116 E, T. Quayle; 



possess remarkable control over their rate of transpiration, such? 

 that at the first hint of drought pressure, they declare a state 

 of siege by closing their stomata. Assuming that they do this 

 during the first warmth of spring they will contribute little to- 

 wards the humidity of the atmosphere during the periods of 

 east to north winds and falling barometers preceding the ap- 

 proachng " lows." They are too much on the defensive to aid- 

 in rain production. 



This is,, however, not the case with growing crops, such as- 

 wheat, oats, etc., which obviously wilt in the hot winds, or with 

 most of the grasses. As one of the main objects of cultivation in 

 the dry areas is to store moisture in the soil for the use of the 

 growing cereal crops, it is almost essential for successful crop- 

 ping that the land should lie fallow for twelve months, and be 

 occasionally worked to prevent weed growths dissipating the 

 water content of the subsoil, and, as this is drawn upon most in 

 the spring months, the plants must then transpire freely. They, 

 therefore, contribute generously to the atmospheric humidity, and 

 so aid in producing conditions favourable for rain. This rea- 

 soning suggested a test. If this is correct, stations in the older 

 Mallee areas, or those in the south-eastern edge of the cultiva- 

 tion area, which is gradually increasing by encroachment upon 

 the Mallee in a north-westerly direction, might be expected ta 

 show some slight improvement in their spring conditions as com- 

 pared with old stations beyond which no great advance has yet 

 been made. This might be shown by rainfall or temperature, 

 or by both. 



To test the matter, the following groups of stations were- 

 chosen : — Tyrrell Downs, Swan Hill, and Kerang to represent the 

 remoter and least benefited portion; Charlton, Lake Marmal and 

 Wychitella South, the area which might be the gainer from the 

 substitution to north-westward of cereal crops and grass for 

 Mallee scrub. The area separating the two groups is about 55 

 miles across. Kerang was assumed to be too far north to bene- 

 fit, but both that station and Swan Hill are south-east from areas, 

 being rapidly developed by irrigation, and should be in a dif- 

 ferent category in the years to come. All of these stations have 

 rainfall records as far back as 1885, and this was chosen as the 

 starting point. Comparisons were made of the mean rainfalls 

 for the three following decades, 1885-94, 1895-1904, 1905-1914. 

 The results were quite favourable to the theory. Two groups of 

 spring months were chosen — September and October, and 



