62 



NATURE 



{Nov. 17, 1887 



good to eat, and called the " Blewit." Agaricus subpul- 

 'verulentus, Pers., is also not uncommon, and several 

 others are known. 



In the spring, fairy-rings have been found containing 

 Agaricus gambosus, Fn, an edible mushroom known in 

 England as the " St. George's mushroom," and much 

 esteemed on the Continent. 



There are also o.ther forms, several of them poisonous, 

 or at least inedible or dangerous ; and even puff-balls 

 are known to be associated with fairy-rings. 



•And now we come to the question, How do these fairy- 

 rings arise and increase? It cannot be wondered at that 

 the people of earlier days, wishing to explain a pheno- 

 menon which none could overlook, sought for satisfaction 

 in their myths and folk-lore, and believed them to be 

 *' caused " by fairies and elves and other mystic beings of 

 the woods and fields, dancing in circles beneath the 

 moonlight, and enchanting the ground into a richness 

 which it did not previously possess. 



Then came the era of science, and people were dis- 

 satisfied with beliefs, and in course of time the followers 

 of De CandoUe at least tried to solve the problem ac- 

 cording to what was known of Nature. It was at least 

 necessary to explain (i) why the centre of the ring is so 

 poor, (2) why the fungi are confined to the margin, and 

 (3) why the ring goes on enlarging, as continued observa- 

 tion showed that it did. 



The first theory of any merit was, that the " ring " 

 takes its origin from a single mushroom, which sheds its 

 spores from the gills down on to the ground around the 

 thick stem : this necessarily produces a ring of spores, 

 as the stem dies down in the centre. Now the physio- 

 logists of those days believed that a plant excretes 

 into the soil at its base substances which are harmful 

 to its further development, and so, they argued, the soil 

 on the inside of the ring of spores is poisoned, as 

 it were, and only the outer spores produce new plants. 

 The new mushrooms come up in a ring, and in their 

 turn shed spores in a ring of rings ; but since the soil on 

 the inside of all these rings is poisoned by the excreta, 

 only the outer series can germinate and grow, and thus 

 a new ring arises next season, and so on. But, it was 

 thought, though the excreta are injurious to the growth 

 of the same plant (the fungus in this case) in that par- 

 ticular soil, other plants can grow there (in the present 

 instance, grasses), and so a ring of rank grass follows on, 

 which in its turn spoils the soil for its own kind as it 

 increases. 



Now it has to be admitted that there was much in- 

 genuity in this hypothesis, and it was maintained for 

 some time ; until, in fact, physiologists had to give up 

 the excretion theory as not in accordance with observed 

 facts. 



Then followed the beginnings of the celebrated doc- 

 trine of the rotation of crops, and the facts accumulated 

 about fairy-rings had to be looked at again. They had 

 become too much for the excretion theory ; how did they 

 look when regarded from the new point of view ? First, 

 however, we may bear in mind the fact noticed by several 

 observers. When two fairy-rings gradually extend so as 

 to interfere, the green circles coalesce and form a single 

 ring : evidently the conditions of the soil in the wake of 

 the advancing ring are such that the grass of another 

 advancing ring cannot go on luxuriating there. It is true 

 this fact was as easily made use of by those who main- 

 tained the excretion theory as by those who advanced 

 the theory we are now going to examine. 



It gradually came to be recognized that the reason one 

 species of plant cannot be continually grown on the same 

 soil was not because the first crop poisons the soil by 

 leaving injurious excreta behind it, but because it takes 

 away certain mineral substances in such proportions 

 that too little is left for the well-being of a second 

 crop of the same species ; in other words, it exhausts 



the soil of certain necessary ingredients. A crop of 

 some other species may be raised on the partially e.<- 

 hausted soil, however, provided it is a plant which does 

 not need the materials now deficient, in such large 

 quantities as its predecessor. This is, roughly sketched, 

 the rationale of the doctrine of the rotation of crops, and 

 it was subsequently suggested that the " fairy-rings " we 

 are considering are a natural illustration of this. The 

 vegetable physiologists then came to the conclusion that 

 the fungus causes the fairy-ring by exhausting the soil of 

 certain substances which are necessary to its existence, 

 and is only able to produce continued crops by extending 

 centrifugally into soil which still yields these substances : 

 the grass, however, does not need these substances in such 

 large proportions, and so follows the fungus. But, as we 

 have seen, the grass which immediately follows the fungus 

 is particularly rank and luxuriant, and it was necessary to 

 find an explanation for this fact. It was then suggested 

 that the dying mycelium of the fungus acts as a manure 

 for the grass to feed upon, and until this is exhausted the 

 growth is peculiarly rich and rampant. 



Before leaving this part of our subject, it should be 

 pointed out that Dr. Wollaston, in an essay on fairy-rings 

 published in the Philosophical Transactions of the Royal 

 Society so long ago as 1809, ventured on the explanation 

 that the fungi spread in rings, because the soil was, by 

 their mycelium, progressively " exhausted of some pecuhar 

 pabulum necessary for their production. . . . An appear- 

 ance of luxuriance of the grass would follow as a natural 

 consequence, as the soil in the interior of a circle would 

 always be enriched by the decayed roots of fungi of the 

 preceding year's growth." 



Meanwhile, the physiology of plants was passing into a 

 more scientific phase of existence, and the beginnings of 

 modern agricultural chemistry were made; and in 1846 

 an important contribution to our knowledge of fairy-rings 

 v/as afforded by Way, who chemically analyzed the soil, 

 the herbage, and the fungi of some of these curious forma- 

 tions. This chemist found that the fungi of his fairy- 

 rings were remarkably rich in phosphoric acid and in 

 potash ; and that they also contained relatively large 

 quantities of nitrogen. We know now that this is true of 

 fungi generally, but these facts were by no means so well 

 understood at that time. Way also analyzed the grasses 

 composing the ring, and found that they also contained a 

 larger proportion of phosphoric acid and potash than the 

 herbage in the neighbourhood, but by no means so much 

 as the fungi : the grass also contained considerable 

 quantities of nitrogen. 



The net result of these investigations was to explain 

 fairy-rings as an illustration of the rotation of crops, but of 

 course putting the explanation on much firmer grounds. 

 Way also pointed out that as the rank green grass was 

 cut or otherwise removed, valuable ingredients (phos- 

 phorus, potassium, alkalies, &c.), were removed with it, 

 and so the crops of grass further inwards become poorer 

 and poorer, accounting for the bare patches often found 

 inside the dark ring. 



Messrs. Lawes and Gilbert, whose magnificent experi- 

 ments on the vegetation of agriculture will never be 

 forgotten, supported the above view of the matter, and 

 showed that the dark-green colour of the rank grass is 

 due to the relatively large quantities of nitrogen. It was 

 at this time (about 1850) customary to suppose that 

 plants obtained their nitrogen from the atmosphere, a 

 view now known to be erroneous from the brilliant re- 

 searches of Boussingault, and of Lawes and Gilbert 

 themselves. On this supposition the extraordinary accu- 

 mulation of nitrogen (in the fungus and rank grass) was 

 thought probably due to a power on the part of the fungus 

 of taking nitrogen from the air. Subsequently the whole 

 matter was again taken in hand by Messrs. Lawes and 

 Gilbert, and the results published in the Journal of the 

 Chemical Society, 1883. 



