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, whether 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., Sc.
THE discovery of specimens of Polyporus 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 (Fr.) has its fellow in
Polyporus rutilans (Fr.), and the likeness is occasionally so great
that some authors have regarded them as varieties of one species.