126 FAIRY RINGS. 



to see, how that soil could ever regain them by repose. 

 But if we suppose the deposit of poisonous exuvise in the 

 soil, by these plants, we can understand how time, reac- 

 tions, and soaking rains, may remove them, and again 

 permit a reproduction, where, for a time, it is prevented. 

 A curious exemplification of the poisoning of the soil 

 against their own growth is afforded by the fungi which 

 have so lately preyed on the potato-crop. In Ireland the 

 potatoes grow much better in the subsequent year, when 

 the diseased potatoes ,have been left to rot in the soil, than 

 when they are carefully removed. 



We have other analogies for this idea. Macaire, who 

 has given much scientific attention to the effect of plants 

 upon soils, observes, that certain vegetables enrich the 

 earth by their exuviae, as, for example, the leguminous 

 vegetables excrete much mucilage, and thus fertilize it for 

 the graminese, but that the papaveraceae injure the soil by 

 the deposit of opiate-like substances, and thus prevent or 

 render growths imperfect. So is it with the peach and 

 bitter-almond trees, which, as well as other plants, that 

 produce prussic acid and the poisonous hydrocyanates, 

 render the soil in which they grow incapable of succes- 

 sive crops of the same kind of trees. A nursery in which 

 young peach trees have been planted, and from which they 

 have been soon removed, will not sustain the same kind of 

 stock for eight or ten years afterwards.* Nature thus se- 

 cures a variety, by a succession of dissimilar vegetations. 

 I might multiply examples; but these are enough for our 

 present purpose. In this way are the fairy rings formed, 

 and in this way are the grasses protected from the end- 



* Manuring the soil from which a peach tree has been removed, does 

 not mend the matter j removal of the soil, or long repose, will alone suffice. 



