206 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



y^ for this distribution is 28-3. The value of P is beyond the range of the 

 usual tables, so that there is no question about the significance. 



(e) The Significance of the Association of Frog-ponds with the 

 Chemical Composition of the Water 



Only the significant associations are given here. Other tables showing the 

 absence of relations w^ith other ions are in the 1939 paper. The corre- 

 spondence w^ith chance in these cases was very close. 



Votassmm 

 The level chosen for testing was 1 8 parts per million. 



y^ for this distribution is 31-6, and so is beyond the range of tables. 



Carhonate 

 The level chosen for testing was 30 parts per million. 



'^ for this distribution is 8-7. This is significant at more than the o-oi level. 

 (There are numerical errors in the table on p. 11 of the 1939 paper, fortunately 

 with no effect on the conclusions.) 



(/) Significance of the Difference in the Phosphate Content of 

 Spawn and Non-spawn Ponds 



In this case, there were numerous analyses of the two groups of ponds. The 

 principal interest centres on the values in the last three weeks of March, when 

 most of the spawning occurred. Tested by calculating t, which was 5-8, 



