12 INTRODUCTION TO THE STUDY OF FUNGI 



it sometimes forms thick Laminae many inches broad in old 

 trunks, but in warmer countries it develops into a spongy- 

 mass, called Xylostroma in past times. These masses will fill 

 up holes in a log nearly as thick as the wrist, and a foot or 

 two in length, or they will spread in layers of an inch in 

 thickness, a foot in breadth, and several feet long. The whole 

 mass is made up of interwoven threads, almost as dense as cork 

 when felted together, but wholly barren, so that it is uncertain 

 whether they are the mycelium of a Polyporus or an Agaric. 

 Having been furnished with a redundant supply of nutriment, 

 they never advance beyond the vegetative stage. In the case 

 of entomogenous Fungi, the mycelium will replace the whole 

 of the tissues, even to the legs and feet, so as to form a com- 

 plete cast of the insect, of which only the dermal covering 

 remains unchanged. In such genera as Cordyceps and Empusa 

 the filamentous structure is only seen in the earliest stage ; 

 this soon gives way to a compact granular mass. The mycelium 

 of the Mucedines, or moulds, when abundantly supplied with 

 moisture, develop rapidly and vigorously, but do not proceed 

 with the fructification whilst the nutriment supplied is abnor- 

 mally great. The conidial stage of the Erysvphei will furnish 

 examples of a thin superficial mycelium adhering by haustoria. 

 In these cases a thin white web runs over the surface of living 

 leaves, as in the vine mildew, and a mildew on the leaves of 

 the maple, but it does not penetrate deeply into the tissues of 

 its host, which it injures by choking up the stomata. Another 

 superficial mycelium is that of Fumago, which forms black 

 patches on the leaves of the lime and other trees, being especi- 

 ally vigorous on those subject to honey-dew. In the sphaeria- 

 like or capsular Fungi, the mycelium is confined, usually, to a 

 few delicate threads at the base of the perithecia, but there 

 are exceptions to this in some superficial species, where a 

 subiculum or conidia-bearing mycelium is present. 



Another form assumed by mycelia is that condition whicli 

 has long been known under the name of Rhizomorpha, when it 

 was suspected to be an independent Fungus, although no form 

 of fruit had been discovered. It is now admitted that the 

 several species are only the vegetative condition of other Fungi. 

 One kind may be seen running between the bark and wood oi 



