64 FUNGI IN PAIRS. 



has been found that, with the exception of a gross-feeding crop 

 like cabbages, or a crop specially rich in albuminoid like red clover, 

 none of the ordinary crops of the farm responds to sulphate 

 manuring. In spite of loss by drainage therefore a supply of 

 sulphate in the soil, sufficient for most crops, is maintained. 



There are two sources of supply of sulphate in the soil. In 

 the first place, Berthellot and Andre shewed that the total 

 amount of sulphur in the soil was nearly eight times that in the 

 form of sulphate, the greater part being in the form of sulphur 

 •compounds produced by the decay of vegetable matter. Mr. 

 Hughes and myself found that these in the presence of certain 

 micro-organisms were converted by atmospheric oxidation into 

 sulphuric acid. In the second place the supply of sulphate is 

 maintained by rain. At Chelmsford the sulphuric acid thus 

 supplied in a year of average rainfall was found to amount to 

 50 lbs. per acre, i.e. more than the average crop could require. 



The sulphuric acid, w 7 hether produced by fermentation in the 

 soil or supplied by rain, combines with the lime of the soil, pro- 

 ducing sulphate of lime. It is owing to this constant exhaustion 

 of the lime of the soil that dressings of lime have to be applied 

 from time to time, and in the absence of such dressings on London- 

 clay soil the land becomes impossible to cultivate. We may 

 suppose that the liming of land has been carried on for centuries. 

 Is it not conceivable that a part of the sulphate of lime that 

 hardens the water, and crystallizes out as selenite in the super- 

 ficial strata of the London-clay, may be due to the inter-action of 

 sulphuric acid and lime in the surface soil ? 



FUNGI IN PAIRS. 



By M. C. COOKE, LL.D., M.A., A.L.S., &c. 



THE discovery of specimens of Poly poms nidulans growing on 

 a tree near Loughton Station, at the last Fungus Foray, 

 has reminded me of several instances in which two species of 

 Fungi, that are closely allied, appear to be good and 

 characteristic species in their extreme forms, but approximate 

 so closely in other instances that it is almost impossible, some- 

 times, to determine to which of the two species the specimens 

 should be referred. Polyporus nidulans ' v Fr.) has its fellow in 

 Polypovus nitilans (Fr.), and the likeness is occasionally so great 

 that some authors have regarded them as varieties of one species. 



