9O PHYSIOLOGY. 



not true roots, they function as roots, or root hairs, in the ab- 

 sorption of food materials. In old cellars and on damp soil in 

 moist places we sometimes see fine examples of this vegetative 

 part of the fungi, the mycelium. But most magnificent examples 

 are to be seen in abandoned mines where timber has been taken 

 down into the tunnels far below the surface of the ground to 

 support the rock roof above the mining operations. I have 

 visited some of the coal mines at Wilkesbarre, Pa., and here on 

 the wood props and doors, several hundred feet below the surface, 

 and in blackest darkness, in an atmosphere almost completely 

 saturated at all times, the mycelium of some of the wood-destroy- 

 ing fungi grows in a profusion and magnificence which is almost 

 beyond belief. Fig. 80 is from a flash-light photograph of a 

 beautiful example 400 feet below the surface of the ground. 

 This was growing over the surface of a wood prop or post, and 

 the picture is much reduced. On the doors in the mine one can 

 see the strands of the mycelium which radiate in fan-like figures 

 at certain places near the margin of growth, and farther back the 

 delicate tassels of mycelium which hang down in fantastic figures, 

 all in spotless white and rivalling the most beautiful fabric in the 

 exquisiteness of its construction. 



190. How fungi derive carbohydrate food. The fungi being devoid of 

 chlorophyll cannot assimilate the CO 2 from the air. They are therefore 

 dependent on the green plants for their carbohydrate food. Among the 

 saprophytes, the leaf and wood destroying fungi excrete certain substances 

 (known as enzymes) which dissolve the carbohydrates and certain other 

 organic compounds in the wobdy or leafy substratum in which they grow. 

 They thus produce a sort of extracellular digestion of carbohydrates, con- 

 verting them into a soluble form which can be absorbed by the mycelium. 

 The parasitic fungi also obtain their carbohydrates and other organic food 

 from the host. The mycelium of certain parasitic, and of wood destroying 

 fungi, excretes enzymes (c.ytase) which dissolve minute perforations in the 

 cell walls of the host and thus aid the hypha during its boring action in 

 penetrating cell walls. 



NOTE. Certain wood destroying fungi growing in oaks absorb tannin 

 directly, i.e. in an unchanged form. One of the pine destroying fungi 

 (Trametes pint) absorbs the xylogen from the wood cells, leaving the pure 

 cellulose in which the xylogen was nitrated; while Polyporus mollis absorbs 

 the cellulose, leaving behind only the wood element. 



