VEGETABLE EXCRETIONS. 55 



menon oi fairy rings, as they are called, that is 

 of circles of dark green grass, occurring in old 

 pastures : these Dr. Wollaston has traced to the 

 growth of successive generations of certain yk?*^?, 

 or mushrooms, spreading from a central point.* 

 The soil, which has once contributed to the sup- 

 port of these fungi, becomes exhausted or dete- 

 riorated with respect to the future crops of the 

 same species, and the plants, therefore, cease 

 to be produced on those spots ; the second year's 

 crop consequently appears in the space of a 

 small ring, surrounding the original centre of 

 vegetation ; and in every succeeding year, the 

 deficiency of nutriment on one side necessarily 

 causes the new roots to extend themselves solely 

 in the opposite direction, and occasions the circle 

 of fungi continually to proceed by annual en- 

 largement from the centre outwards. An appear- 

 ance of kixuriance of the grass follows as a na- 

 tural consequence ; for the soil of an interior 

 circle will always be enriched and fertilized with 

 respect to the culture of grass, by the decayed 

 roots of fungi of the preceding years' growth. 

 It often happens, indeed, during the growth of 

 these fungi, that they so completely absorb all 

 nutriment from the soil beneath, that the her- 

 bage is for a time totally destroyed, giving rise 

 to the appearance of a ring bare of grass, sur- 



* Phil. Trans, for 1807, p. 133. 



