Atkins and Lebouu — Hydrogen ton Oonceniration of the iSoil. 235 



The results of Table 2 are shown graphically in figs. 1 and 2. 



The record of //. virgata, 9 at pH 6 5, must be explained. One was found on 

 acid soil near the sea, the situation being exposed to blown spray, so it must 

 have been close to an alkaline region. The other eight were on bracken and 

 nettles in a coastal situation where alkaline soil, as tested, was within fifty yards, 

 probably less. 



so 

 s-s 



6s 



7-5 



«o 



i 



^H A-o.'^.qtA. (W A^-aXt^J^^Xj^ ri '^^XxiAj^ ri Vv.^i>«Xs X -^^-<V>v«Xci^ l^\£..^xXs\, aXrj^^(A«/wt£_ . 



Fig. I 



It must be pointed out that the bottom line of Table 2 records the number 

 of species for each x>H value, each species being assumed to occur for every 

 value within its extreme range. Thus H. nemoralis, found at x>H 6 and pH 7, 

 is presumed to occur at pll 65 also. 



xS 



xo 



^IS 



10 



S 



jvH jo 45 



1 



6o 



Fig. 2. 



65 70 



to 



Viewed as a record of species of snails for the districts concerned, mainly 

 the Plymouth district and the country round Bray Head, Co. Wicklow, the 

 collection ranks as very imperfect. Sufficient work has, however, been done to 

 show that the pH value of the soil is a factor which is important in regulating 

 the distribution of snails in any district. Certain minute Hyalinias are 



