290 STUDIES OF AMERICAN FUNGI. 



Water. Like all growing plants, the mushroom contains a very 

 large proportion of water. The actual amount 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 com- 

 paratively 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 solu- 

 ble 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 melt- 

 ing point being most abundant. These fatty substances occur in the 

 stem, but are much more abundant in the cap, especially in the fruit- 

 ing portion. Just what nutritive value these fatty matters may 

 have has never been determined. 



Carbohydrates. The largest part of the dry matter of the mush- 

 rooms 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 pro- 

 portion 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 sus- 

 taining 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 cabohydrates 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 matter, Pleurotus ulmarius gives 

 12.6 per cent., and Clitopilus prunulus gives 15 per cent. The aver- 



