94 PLANT HABITS AND HABITATS IN THE 



Rainfall. 



Port Augusta lies just within the 10-inch isohyet, having a rainfall 

 of 9.43 inches, the average for 52 years. The greatest rainfall here 

 recorded for one year, up to and including 1912, was 17.52 inches, 

 and the least was 2.21 inches, the ratio thus being nearly 8 to 1. It is 

 of interest to note that the ratio is about the same as at Copley, but 

 very much greater than at Tarcoola, although the average annual 

 rainfall at all of these places does not vary greatly. The largest pro- 

 portion of the rain falling at Port Augusta, which amounts to about 75 

 per cent of the whole, occurs in the cool season. This is approximately 

 10 per cent less than the rainfall for the corresponding period at Tar- 

 coola and 15 per cent more than Copley. The distribution throughout 

 the year is such as to accentuate the arid conditions for the region, 

 and since rainfall expectancy, the season of its occurrence, and the 

 actual amount are important factors in the aridity of a region, it is 

 seen that Port Augusta must be considered fairly arid. 



Temperature. 



The climate of Port Augusta is characterized by cool winters and 

 hot summers. The latter, as shown above, are also dry. The mean 

 annual temperature is 66.2° F., about 1° less than that of Copley 

 and 2° less than the mean at Oodnadatta. The absolute maximum 

 (28 years' records) is 117° and the absolute minimum is 31.4°. The 

 mean number of days in the year having a temperature above 90° is 

 67.4, and the mean number of nights with a temperature under 40° 

 is 16.6. The monthly course of the temperature at Port Augusta is 

 given in table 7. 



Vegetation. 



The vegetation at and in the neighborhood of Port Augusta, as 

 would be expected from the nature of the physiography of the place, 

 is very diverse, and in earlier, pre-colonial times, must have been 

 fairly abundant. This is indicated not only by the natural flora, but 

 by such introduced plants as have escaped and live under natural con- 

 ditions, or by such cultivated species as grow without irrigation. 

 Among the latter may be mentioned Schinus molle, which occurs in all 

 parts of the town. The species forms an extensive superficial root- 

 system which radiates far from the main stem. Opuntia monocantha 

 also is fairly common and Tamarix crus-gallica occurs about the village. 

 Possibly the most striking introduced plants which reproduce them- 

 selves naturally in the Port Augusta region are species of Mesem- 

 bryanthemum, as M. crystalUnum, which grow on the sandhills near the 

 coast. 



In and close to town several species of shrubs and trees, native to 

 the region, are of interest. In the parks, for example, one finds 

 Acacia rigens and A. salicina, and among other species, Nitraria 



