32 



The AtniosjtiH'rc of tin Soil 



various patches. It is found that there is a perceptible failiug oti of 

 oxygen and rise in COg in jjassing from a neutral matrix to a "sour" 

 patch (indicated by the presence of rumex or in extreme cases by the 

 total absence of all vegetation). But a patch of a sohtary species 

 occurring on a neutral plot such as plot 7 shows no such difference. 

 The results are: 



Samples taken May 24tb, 1913. 



Another held where segregation occurs is Geescroft which is liable 

 to become waterlogged in winter owing to the absence of calcium 

 carbonate from the soil and the consequent deflocculation of the clay. 

 During normal moist or dry conditions the soil air from the various 

 patches is similar in compositioii and resembles that from the other 

 fields. But in ver}' wet conditions marked differences set in, the 

 oxygen falling and the nitrogen^ rising very con.siderably in amount; 

 this happens particularly under the patches of Festuca ovhia the roots 

 of which form a densely matted tangle near the surface, l)ut it is less 

 marked under the patches of Aira caesj)itos(i the roots of which form 

 a bristl}' mass more readily allowing gaseous diffusion. The results are 

 plotted in Fig. 6, they are as follows: 



Wet conditions 



' Bsaminatioii for hydrogen or methane ha^ so far led to negative result* 



