ount present varies greatly in
different species. In the above table it will be seen that _Polyporus
sulphureus_, with over 70 per cent. of water, has the least of any
species mentioned, while the species of _Coprinus_ and _Agaricus_ have
usually fully 90 per cent. water. The amount of water present, however,
varies greatly in the same species at different seasons and in different
localities, and with variations in the moisture content of soil and
atmosphere, also with the age and rapidity of development of the
individual plant.

=Total Nitrogen.=--The proportion of nitrogen in the dry matter of
different species varies from 2 per cent. to 6 per cent. This
comparatively high nitrogen content was formerly taken to indicate an
unusual richness in proteid substances, which in turn led to very
erroneous ideas regarding the nutritive value of these plants. The
nitrogenous substances will be more fully discussed later, when we
consider their nutritive value.

=Ether Extract.=--This consists of a variety of fatty substances soluble
in ether. It varies greatly in quality and quantity in different
species. The amount is usually from 4 per cent. to 8 per cent. of the
total dry matter. It includes, besides various other substances, several
free fatty acids and their glycerides, the acids of low melting point
being most abundant. These fatty substances occur in the stem, but are
much more abundant in the cap, especially in the fruiting portion. Just
what nutritive value these fatty matters may have has never been
determined.

=Carbohydrates.=--The largest part of the dry matter of the mushrooms is
made up of various carbohydrates, including cellulose or fungocellulose,
glycogen, mycoinuline, trehalose, mannite, glucose, and other related
substances. The cellulose is present in larger proportion in the stem
than in the cap, and in the upper part of the cap than in the fruiting
surface. This is doubtless related to the sustaining and protective
functions of the stem and the upper part of the cap. Starch, so common
as a reserve food in the higher plants, does not occur in the mushrooms.
As is the case with the fats, no determination of the nutritive value of
these substances has been made, but it may be assumed that the soluble
carbohydrates of the mushrooms do not differ greatly from similar
compounds in other plants.

=Ash.=--The ash of mushrooms varies greatly. _Polyporus officinalis_
gives but 1.08 per cent. of ash in dry mat