IX.] 



"FAIRY RINGS" 



279 



follows the death of the fungus. In other words, 

 the humus of the soil, slow to decay and nitrify in 

 the usual way, is changed into material undergoing 

 rapid change by its preliminary conversion into the 

 tissue of the fungus. At the same time, as the 

 supply of rapidly acting plant food has been solely 

 derived from the soil, the ultimate result is the im- 

 poverishment of the soil within the ring by the develop- 

 ment of the fungi and the subsequent luxuriant growth 

 of grass. 



The following figures relate to the composition of 

 the soil (mean of five examples) within, on, and outside 

 " fairy rings " : 



It will be seen that the unchanged soil outside 

 contains the most carbon and nitrogen ; the ring itself 

 contains an intermediate amount, and the least is 

 contained within the ring after the luxuriant vegetation 

 has passed away. The soil on the ring is in high 

 condition, because the organic residues it contains are 

 recently formed and will change rapidly ; after they 

 have been cropped out, the land is less able to support 

 a crop, even though there is still much plant food left 

 in the soil. The last column in the table (the analysis 

 of a single example only) shows the difference in avail- 

 able nitrogen ; and though in a pasture there are never 

 many nitrates to be detected, so rapidly are they seized 

 upon by the crop, still the organic nitrogen compounds 

 in the soil must be in a more nitrifiable condition on 



