48 



PLANT HABITS AND HABITATS IN THE 



rains amounting to over "20 points," i. e., 0.20 inch, do real good in an 

 agricultural way. With these and other observations in mind, it has 

 been concluded to lower the minimum and to define an ecologically 

 effective rainfall as one consisting of 0.15 inch, or more, and which 

 occurs in a distinct rainy period. Whether subsequent study wiU 

 establish another minimum does not concern us at present. It will be 

 useful, if for no other purpose, to show how large a percentage of the 

 total annual rainfall in the dry interior is of little or no moment to the 

 native vegetation, and hence how very arid the region really is. 



The effective rainfall for Oodnadatta, Copley, and Quorn was de- 

 termined for a period of five successive years, and the results are pre- 

 sented in table 11. The last column of the table gives also the actual 

 recorded rainfall for each of the years referred to. It will be seen that 



Table 12. — Mean, highest, and lowest monthly rainfall at Oodnadatta, in inches, for a period 



of S6 years. 



