114 BRAMBLES AND BAY LEAVES. 



the roots nor stems of the same plants, when completely detached 

 and immersed, would produce this effect, and hence he concludes that 

 it is an exudation from the roots which takes place only when the 

 plant is in a state of living and healthy growth. Now we can easily 

 understand how it is that plants of one kind will not flourish in the 

 same soil for any length of time. When rooted in the soil, the plant 

 continues to excrete or throw off certain matters which are injurious 

 to it, or which have served their purpose in its economy ; and the 

 soil getting charged with these exudations, becomes at last wholly 

 unfit for the plant which has occupied it, though the principles which 

 proved obnoxious to that one, may be nutritious and desirable for 

 plants of another kind. Hence, in clearing the American woods ic is 

 found, that if the ground is allowed to run out of tillage, the vege- 

 table tribes which formerly occupied it do not spring up again, but 

 trees of another order and different constitution take possession of the 

 soil ; and in the same manner the salicaria flourishes in the vicinity 

 of the willow, and the broom-rape in that of the hemp. 



Of plants which exercise this influence in a special manner, the 

 fungi are among the most prominent ; for wherever any of the tribe 

 take root, they speedily render the soil unfit for their continued 

 growth. The spot thus rendered pernicious to fungous growths is 

 particularly suitable for grasses, and as the fungi disappear, grasses 

 take their place in a rich and luxuriant growth. Here then is the 

 secret of the fairy ring, — the result of one of nature's systems of 

 successive crops. 



To pursue the inquiry a step further, and ascertain why grass in 

 preference to other plants should flourish where mushrooms decay, 

 we have only to analyze the latter plant, and a solution immediately 

 presents itself. The ashes of the various kinds of fungi found in 

 fairy rings, yield in analysis small quantities of silica, lime, mag- 

 nesia, iron, sulphuric acid, carbonic acid, and soda. Potash and phos- 

 phoric acid occur also, but in very large proportions, the first amount- 

 ing to fifty-five per cent, of the entire analysis, and the second to 

 twenty-nine per cent., so as together to constitute the bulk of inor- 

 ganic constituents. Now phosphorus and potash are the finest of 

 manures for grass ; and hence, beside the fact of the soil becoming 

 unfitted for the continuance of fungi, the latter may be partially 

 driven from the field, choked out in fact by the rapid and luxurious 

 growth of grass in the rich soil thus provided for it. 



