100 SAPROPHYTES AND THEIR RELATION TO DECAYING BODIES. 



that their colour is quite altered. The so-called "mushroom-spawn", used in the 

 cultivation of mushrooms, is also nothing but a mycelium, which entirely invests 

 the manure employed in the cultivation of that fungus, and gives it a white 

 mottled appearance. 



In addition to Fungi, however, a number of Mosses, Liverworts, Ferns, Lycopods, 

 and Phanerogams take up organic compounds from the products of decay to serve 

 as their food. 



In deciding whether a plant takes up only the mineral substances rendered 

 soluble by the decomposition of the soil, or only organic substances disengaged 

 by the decay of dead plants and animals, we depend generally on the condition 

 and appearance of the nutrient substratum, and, in particular, on its composition, 

 i.e. whether it is exclusively or predominantly organic. But such observations 

 give a very uncertain indication. For, on the one hand, it is possible for plants 

 rooted in a substratum of decaying matter to take nothing but mineral salts {i.e. 

 inorganic compounds) from it; and, on the other hand, it frequently happens that 

 sand or clay, apparently uncontaminated with organic matter, is saturated by 

 water which oozes from a layer of humus in the vicinity, and brings with it 

 organic compounds in solution. The following facts are instructive with reference 

 to the former of these two phenomena. Maize, barley, and other cereals may be 

 reared in fluids, so prepared as to contain a small quantity of mineral food-salts 

 dissolved in distilled water (12 mg. potassium phosphate, 12 mg. sodium phosphate, 

 27 mg. calcium chloride, 40 mg. potassium chloride, 20 mg. magnesium sulphate, 

 10 mg. ammonium sulphate, and a few drops of iron chloride in a litre of distilled 

 water), all organic compounds being carefully excluded. When the plants germinate, 

 they develop roots which descend in the liquid and absorb from it mineral salts 

 according to their requirements. They produce stems, leaves, flowers, and, ulti- 

 mately, seeds capable of germination. Other plants of maize or barley reared 

 simultaneously in richly-manured ground develop likewise leaves, flowers, and fruit. 

 Moreover, analysis of the ash in both cases reveals the fact that the plants which 

 took their nutriment from the manure contain the same salts as those reared in the 

 made-up solution of salts free from organic compounds. Hence, the conclusion may 

 be drawn that a plant of this kind is capable of obtaining an adequate supply of 

 food-salts equally well, either from earth free from humus and manure, or from 

 humus or manure themselves. The experiment further shows that, in the latter 

 case, organic compounds need not necessarily be absorbed, in addition to the mineral 

 constituents of humus or manure which are disengaged during decomposition. 



We must next refer to a fact in connection with the second point above men- 

 tioned, viz. that plants rooted in sand or loam devoid of humus may yet have 

 organic compounds brought to them by water filtering through a stratum of humus 

 near at hand. The fact in question is, that the very water which one would least 

 expect should contain organic compounds, that, for instance, of cold mountain 

 streams, does very generally include traces of such compounds. On looking through 

 analyses of mineral springs, one finds for the most part, amongst their constituents, 



