[ 233 J 



No. 28. 



THE HYDROGEN ION CONCENTRATION OF THE SOIL AND OF 

 NATURAL WATERS IN RELATION TO THE DISTRIBUTION OF 

 SNAILS. 



ByW. R. G. ATKINS, O.B.E., Sc.D., F.I.C, 



AND 



M. V. LEBOUR, D.Sc. 



[Read June 26. Printed July 27, 1923.] 



It has been shown that the hj^drogen ion concentration of the soil exercises a 

 profound effect upon the distribiition of plants and upon the growth of crops. 

 Accordingly it seemed possible that simUar effects might be observed in the case 

 of animals, such as worms and snails. 



With the object of exploring this possibility, snails were collected in diverse 

 situations. In order to get an idea of the relative abundance of the members of 

 each species, every snail found by careful searching within a small area, about 

 four square feet, was collected without any sort of selection. In the table of 

 results the actual numbers are given. It was considered that this was better than 

 to give the number of situations at which each species was found. The numbers 

 given must not, however, be considered as precise statistical values, but as an 

 attempt to give a rough quantitative record. Many of the more acid sites 

 examined were very poor in snails. 



The hydrogen ion concentration of the soil was determined, for each situation 

 in which snails were gathered, by means of the colorimetric method, as previously 

 employed by one of us (Atkins, 1922) when studying plant distribution. The 

 results are recorded, as is customary, in j^H values. The sjnnbol j)H denotes 

 the logarithm of the reciprocal of the number of grams of hydrogen ion per litre, 



viz., pH = log =j. Only a few observations relate to aquatic species. 



In order to economise space, the pIT vahies of typical soil situations and 

 waters are recorded in Table 1. A detailed account of the determinations and 

 the supposed causes of the reactions found is given in the paper already 

 mentioned. 



It may be mentioned that the R. Yealm, where examined, supports Asellus 

 aquaticus, but not Gammarus pulex. The latter crustacean abounds, however, 

 in the alkaline streams of the district. In water from these it can live and 

 breed in smaU glass vessels, but when placed /in the R. Yealm water it has 

 invariably died. 



Determinations of soil 2)H values are made to pH 01, but in tabulating the 

 values obtained, the results ai'e grouped to nearest pH 05. In doing this, 

 pH 6-8-7-2 is called pH 70, and pH 7-3-7-7 is given as pH 7-5. 



SCIENT. FKOO. K.D.S., VOL. XVII, NO. 28. 2 X 



