Feb. 2 1, 18S4] 



NA TURE 



385 



their more limited power of obtaining nitrogen, could not 

 appropriate from the soil. They assumed that it was the 

 nitrogen rather than the mineral constituents of the fungi 

 to which the manuring action was mainly to be attributed, 

 and in this they were right ; but the theory has required 

 some correction nevertheless, inasmuch as they have 

 since proved the source of nitrogen in the fungi to be the 

 soil, not the atmosphere. 



As doubts were entertained at first on this point, 

 direct experiments were tried at Rothamsted, and in 1 874 

 samples of soil were taken within a fairy ring, immediately 

 upon it, and outside, and these yielded on analysis the 

 lowest percentage of nitrogen in the soil within the ring, 

 a higher percentage under the ring, and a higher still 

 outside it. The soil therefore had lost nitrogen by the 

 growth of the fungi, and the obvious conclusion was that 

 the fungi possess a greater power than the grasses of 

 abstracting nitrogen from the soil. 



The analyses of the various species of fairy-ring fungi 

 do not greatly differ. Two species occurring at Rotham- 

 sted — Agaricus prunulus and Marasinius orcadiiin — 

 contain nitrogenous compounds to the amount of one- 

 third of their dry substance, the ash being rich in potash 

 and phosphoric acid. Their occurrence on pastures, like 

 that of the common mushroom, is probably due to the 

 manuring of the ground by animals and their continuance 

 and growth depend on certain conditions of soil and 

 season. They are rarely developed on rich soils, or on 

 those which are highly manured, or in seasons favourable to 

 the general herbage of the turf ; and when they do appear 

 under these conditions they will probably not be repro- 

 duced, or only in patches. The recent wet seasons have 

 dispersed fairy rings in situations where they have usually 

 proved persistent. They prevail wherever the growth of 

 the grasses is inferior, especially on the poor downs of the 

 chalk districts, and on poor sandy soils where the natural 

 herbage is wanting in vigour. 



The history of fairy rings, as it has now been written 

 at Rothamsted, will attract close attention from all who 

 are interested in the nutrition of plants, including the 

 student of agriculture, and all, in fact, who are specially 

 concerned in the question of the food supply. It was not 

 previously known that any kind of plant could feed directly 

 on the organic nitrogen of the soil itself. It was recog- 

 nised that the root-development of plants differed, and 

 that the greater e.xtension of their roots enabled some 

 plants to secure a larger proportion of the constituents of 

 the soil than others. But here is a race of plants pos- 

 sessing quite unsuspected powers of assimilation ! In- 

 stead of rising from the ashes of the phoenix they feed 

 upon its undecayed body, that is, upon the organic 

 nitrogen of the soil. The Leguminosae, for example, 

 such as beans and clover, are known to assimilate more 

 nitrogen from a given soil than the Graminea;, such as 

 wheat and barley, and this has been attributed to absorp- 

 tion by their leaves, or to the superior development of 

 their roots. Another alternative is now suggested, and 

 possibly a new departure may be taken in the science of 

 agriculture, as the result of the recent discoveries in 

 connection with fairy rings. Henry Evershed 



A CHEAP INSULATING SUPPORT 

 T NSULATING-SUPPORTS are so indispensable in the 

 *■ work of an electric laboratory that several forms have 

 come into extensive use. The plan devised by Sir W. 

 Thomson for securing high insulation by surrounding a 

 glass stem with concentrated sulphuric acid to absorb the 

 moisture which otherwise would condense from the air 

 and form a conducting film over the surface of the glass 

 is remarkably efficient, and has many advantages. Modi- 

 fications of this form of insulator have been largely used 

 by Prof Clifton, F.R.S., in the Clarendon Laboratory, and 

 by Profs. Ayrton and Perry in the laboratories of the 

 Technical College at Finsbury. Another tnodification 



due to M. Mascart, was described in Nature, vol. xviii. 

 p. 44; and this pattern has come into extensive u-e 

 under the name of the support isohxnt Mascart. Though 

 excellent in every way it is very expensive, as its manu- 

 facture necessitates a special piece of glass-blowing. The 

 central support of glass is solidly fused into the bottom of 

 a glass vessel with a very narrow neck into which acid is 

 poured through a tubulure at the side. 



The insulating support which I have recently described 

 before the Physical Society of London is a much simpler 

 affair, and can be made very quickly and cheaply froii 

 the materials at hand in every laboratory. The figure 

 shows the form of the support. A wide-mouthed glass 

 bottle, E, about 10 cm. high, and from 5 to 6 cm. diameter, 

 is selected. A piece of stout glass tubing about 20 cm. 

 long is then taken. One end is closed in the blowpipe 

 flame, and blown into a thick bulb ; and while yet hot the 

 bulb is flattened, so as to form a foot for the stem. The 

 flattened bulb should be as large as is compatible with its 

 insertion into the mouth of the bottle. To hold it in its 



place some paraffin wax is melted in the bottle— from 50 

 to 70 grm. is quite sufficient — and when it has cooled so 

 as nearly to have become solid the stem, previously 

 warmed, is inserted. When cool, the paraffin holds the 

 stem firmly in its place. To keep out the dust a disk cut 

 out of sheet guttapercha is fitted on as a lid. If dipped 

 into hot water for a minute it can be moulded to the 

 required form. It fits loose-tight upon the stem, as shown 

 at C, and when the stand is not in use is slid down over 

 the mouth of the bottle. A brass disk, a, having a short 

 brass stem, B, below it, slips into the upper open end of 

 the tube, and forms the top of the stand. It is also found 

 convenient to make from rods of glass other supports, 

 shaped at the top in the form of hooks, which can be 

 slipped down into the central tube. These are very useful 

 for holding up wires that pass over the experimenting 

 table and require to be well insulated. The bottle is let 

 into a wooden foot, G. In cases where very perfect insu- 

 lation is required I have poured a little strong sulphuric 

 acid into the bottle above the paraffin. In practice, how- 

 ever, the insulation of the paraffin is amply sufficient for 

 most purposes, provided dust is properly excluded. 



SiLVAXUS P. THOiMPSON 



JOHN HUTTON BALFOUR 

 T N Prof. Balfour, whose death we announced in our 

 •*• last issue (p. 365), has passed away another of that 

 group of eminent teachers, including Goodsir, Syme 



