312 FIRST FORMS OF VEGETATION. 
vegetation consist of -greyish-white interlacing 
filaments, forming a flocculent net-like tissue, and 
penetrating and ramifying through the decaying 
substances on which the mushroom grows. These 
filaments are formed of elongated colourless cells. 
They are developed under ground, and in other 
plants would be called roots. This part of the 
fungus is called by botanists mycelium, and is 
Fic. 29.—Parts or MusHroom (Agaricus procerus). 
(a) Pileus or Cap. (4) Hymenium or Gills. (c) Annulus. (d) Stipe or Stalk. 
(e) Volva. (/) Mycelium or Spawn. (g) Spores. (4) Basidia. 
popularly known as the spawn by which the 
mushroom is frequently propagated. In favour- 
able circumstances this mycelium spreads with 
great rapidity, sometimes, especially when pre- 
vented from developing organs of reproduction, 
attaining enormous dimensions. It may be kept 
dormant, in a dry state, for a long time, ready to 
grow up into perfect plants when the necessary 
