September 1, 1899.] 



KNOWLEDGE. 



197 



purely artificial classification is ill-adapted to the 

 conditions presented by a class of organisms like the 

 Foraminin'ra, largely made up of groups of which the 

 modifications run in parallel lines. This ' isomorphism ' 



exists not merely between a single series 



in one of the larger divisions, and a single series in 



another, but often amongst 

 several series, even of the 

 same family. It not unfre- 

 quently happens that a 

 member of one group pre- 

 sents a greater similarity to 

 its isomorph in another 

 group with which it has no 

 relationship than it does to 

 any other member of its 

 own group. Take a familiar 

 illustration ; suppose the 

 fingers of the two hands to 

 represent the modifications 

 (species) of two such parallel 

 types of Foraiiiinifcra : the 

 thumb of one hand resembles 

 more closely the thumb of 

 the other hand than it does 

 any other of the lingers of 

 its own." 



A comparison of the 

 marsupial quadrupeds of 

 Australia and South America 

 with the placental mammals 

 of the rest of the world pre- 

 sents another series of these 

 isomorphs. There are certain 

 Marsupials which seem set 

 over against the Carnivora, 

 others against the Kodents, 

 and so forth. Mr. Murray, 

 in his " Geographical Dis- 

 tribution of Mammals," has 

 figured on the same page 

 two animals, one a small 

 placental mouse, and the other a small marsupial mouse, 

 and their outward forms are almost indistinguishable ; and 

 yet the common parent of the two forms must be sought, 

 according to our present notions of phylogeny, before the 

 separation of the two great groups of Quadrupeds. 



Another instance of isomorphs occurs in the two parallel 

 groups of the Iridem and the Liliacere. Every one knows 

 how closely similar in outward appearance are the purple 

 crocus of the spring and the purple colchicum of the autumn ; 

 and yet the crocus is more nearly related to the yellow iris 

 than to the colchicum ; and the colchicum is more akin to 

 the garlic or the Butchers' broom than to the crocus. 



It seems as if when two lines of development started 

 from a common point, they sometimes carried in gmnio the 

 necessity of development along the same lines, and the 

 production of Uke form at corresponding points in the 



divergent courses. 



♦ 



FAIRY RINGS. 



By A. B. Steele. 



THE green circles, or parts of circles, in pastures, 

 popularly known as fairy rings, have given rise to 

 many curious beliefs and sayings, and their 

 marvellously rapid growth has struck the un- 

 cultivated as a supernatural phenomenon. The 

 prevalent belief was that they were caused by the midnight 



Fia.22. — ToblsphonaijUum 

 violaeeum. a and b successive 

 stages in ripening of Sporan- 

 gium. (After Bref eld.) 



dancing and revelry of the fairies ; and Shakespeare speaks 

 of the elves — 



" Whose pastime 

 Is to make midnight mushrooms." 



In the west of England these rings are called " hag's 

 tracks." In the myths and folk-lore of Sweden they are 

 said to be enchanted circles made by fairies. The elves 

 perform their midnight stimm, or dance, and the grass 

 produced after the dancing is called ailfeximj. A belief 

 prevails in some parts of this country that anyone treading 

 within the magic circles either loses consciousness, or cannot 

 retrace his steps. Many absurd theories have been pro- 

 pounded as to the cause of these rings. Aubrey, who 

 wrote the " Natural History of Wiltshire," in the seven- 

 teenth century, says that they are generated from the 

 breaking out of a fertile subterraneous vapour, which 

 comes from a kind of conical concave, and endeavours to 

 get out at a narrow passage at the top, which forces it to 

 make another cone, inversely situated to the other, the 

 top of which is the green circle. Another remarkable 

 theory by a writer, quoted in Captain Brown's notes to 

 White's " Selborne,'' attributes these rings to the droppings 

 of starlings, which, when in large flights, frequently alight 

 on the ground in circles, and are sometimes known to sit 

 a considerable time in these annular congregations. It 

 was also thought that such circles were caused by the 

 effects of electricity, and for this belief the withered part 

 of the grass within the circles may have given foundation. 

 Priestley was a strong advocate of the electric theory, and 

 was supported by many eminent men of his time. 



" So from the clouds the playful lightning wings, 

 Riyes the firm oak, or prints the fairy rings," 



says Dr. Darwin, and appends a note that flashes of 

 lightning, attracted by the moister part of grassy plains, 

 are the actual cause of fairy rings. ArchiBologists suggested 

 that they might be the remains of circles formed by the 

 ancient inhabitants of Britain, in the celebration of their 

 sports, or the worship of their deities. Naturalists formerly 

 came to the conclusion that the rings were caused by 

 the underground workings of insects, and a few years ago 

 a writer in the "Transactions of the Woolhope Club" 

 attempted to prove that they were the work of moles. 



These so-called fairy rings, which have long puzzled 

 philosophers, are caused by a peculiar mode of the growth 

 of certain species of fungi, the peculiarity being their 

 tendency to assume a circular form. A patch of spawn 

 arising from a single seed, or a collection of seeds, spreads 

 centrifugally in every direction and forms a common felt 

 from which the fruit rises at its extreme edge ; the soil in 

 the inner part of the disc is exhausted, and the spawn dies 

 or becomes effete there while it spreads all roimd in an 

 outward direction and produces another crop, whose spawn 

 spreads again. The circle is thus continually enlarged 

 and extends indefinitely until some cause intervenes to 

 destroy it. This mode of growth is far more common than 

 is supposed, and may be constantly seen in our woods, where 

 the spawn can spread only in the soil or among the leaves 

 and decaying fragments which cover it. In the fields this 

 tendency is illustrated by the formation of circles or parts 

 of circles of vigorous dark green grass. To get at the 

 cause, however, of the rank growth of the grass composing 

 these rings, is not without its difficulties still. It is known 

 that fimgi exhaust the soil of plant-food and store it up 

 in their own substance. In the case of these fairy rings 

 they take up from the soil organic nitrogen which is not 

 available to the grasses, and in some way become the 

 medium of the supply of the soil-nitrogen to the grasses 

 forming the circle. How exactly the nitrogen, one of the 

 most important plant-foods, is fixed by these fungi, has 



