OCCURRENCE OF " FAIRY-RINGS." 19 



under equal conditions of ripeness contains a comparatively low 



percentage of nitrogen) that is so strikingly developed under the 

 influence of nitrogenous manures ; whilst the Leguminous her- 

 bage, which is characterized by a very high percentage of nitro- 

 gen, is specially developed by mineral manure containing potass ; 

 and when to this nitrogenous manures (especially ammoniacal) 

 are added, the plants of the Leguminous order are almost abolished. 

 These striking results, brought out in experiments on the 

 mixed herbage of grass-land, are moreover perfectly consistent 

 with those observed in the growth of individual Graminaceous 

 and Leguminous crops in rotation on arable land. Thus, a crop 

 of wheat, barley, or oats is, other things being equal, very much 

 increased by nitrogenous manures. A crop of clover or beans, 

 on the other hand, although it may yield three, four, or five times 

 as much nitrogen over a given area, as a crop of wheat, barley, or 

 oats growing on the same description of land, is not characteris- 

 tically benefited by direct nitrogenous manures. But these Le- 

 guminous plants will develop and assimilate an enormous amount 

 of nitrogen under conditions in which the Graminacese would Ian- 

 guish, and they at the same time leave the land in improved con- 

 dition for the growth of the Graminaceae. It must be admitted 

 that the source of the much larger quantity of nitrogen assimi- 

 lated over a given area by plants of the Leguminous than of 

 the Graminaceous family, and of the residue of it left by them in 

 the upper layers of the soil in a condition available for the Gra- 

 minacese, is not yet conclusively explained. 



Reflecting upon these facts, Mr. Lawes and myself have often 

 felt that if we could determine the source of the nitrogen of the 

 fungi growing in "fairy-rings," some light might perhaps be 



thrown on the question of the source of the nitrogen of the Legu- 

 minosse which we cultivate separately in rotation, or which grow 

 in association in the mixed herbage of grass-land. 



It will be readily understood that the nearly twenty conditions 

 as to manuring, and the as many different conditions as to flora, 

 which the experimental plots in the Park at Rothamsted offer, 

 afford an extremely favourable opportunity for observing the con- 

 ditions, both as to manure and association, under which fungi, 

 and especially those occurring in the so-called "fairy-rings" most 

 readily develop. Accordingly for some time past Mr. Lawes 

 has observed their occurrence and development ; and it is the 



c2 



