206 THE PLANT WOELD 



FAIRY RINGS. 



By E. M. Williams. 



ON coming to eastern Sontli Dakota eleven years ago, one very 

 noticeable thing about the flora of the prairies was the great 

 number of " fairy rings " to be found on all the uplands where 

 the wild grass sod had not been broken. These rings were from one to 

 fifty feet or even more in circumference, and in more or less perfect cir- 

 cles which could be seen at considerable distances because of the level 

 country and the clearness of the atmosphere. The grass is a much 

 darker green inside than outside the ring, and also grows much more 

 luxurianth^ in these spots, particularly toward the outer edges. Occa- 

 sionally toward the center of very large rings the grass ls not much 

 darker than that outside, but is always bordered by a zone of luxuriant 

 dark green grass. These were found to be common all over the eastern 

 and northeastern parts of the State, and probably occur farther w^est 

 also. The rapid settlement of this i)art of the State has brought most 

 of these areas under cultivation, but wherever the wild grass is yet un- 

 disturbed they are to be seen. 



The Fairy Ring Mushroom {Marasmius oreades). 

 Gray Bulletin. 



Reprinted from The Asa 



Such a marked difference in these spots could hardly fail to attract 

 attention, and various reasons have been assigned as to their origin. 

 One student at the college at Brookings, and afterwards at Cornell, who 

 made quite an exhaustive study of these " rings," came to the conclu- 

 sion that they were caused by the growth of one or more large species 

 of puff-ball which are very abundant on the prairies in early spring and 

 sometimes at intervals throughout tlie summer. 



