DIV. I 



THALLOPHYTA 



465 



, Polyporus officinalis, with an irregularly tuberous white fructification, 

 occurs on Larches in South Europe ; it contains a bitter resinous substance and 

 is also used in medicine. The mycelium of Fomes fomentarius, Touch-wood, is 

 parasitic in deciduous trees, especially the Beech, and produces large, bracket 

 or hoof-shaped, perennial fructifications, 30 cm. wide and 15 cm. thick. They 

 have a hard, grey, external surface, but inside are composed of softer, more loosely- 

 woven hyphae, and were formerly used for tinder. The narrow tubes of the 

 hymenium are disposed on the under side of the fructifications in successive annual 

 layers. Fomes igniarius (Fig. 415), 

 which is often found on Oaks, and 

 has a similar structure, has a rusty- 

 brown colour, and furnishes, since 

 it is much harder, a poorer quality 

 of tinder. 



Many parasitic Polyporeae are 

 highly injurious to the trees at- 

 tacked by them ; thus Fomes annosus 

 often causes the death of Pines and 

 Spruce Firs. Merulius lacrymans ( 84 ), 

 the Dry Rot fungus, is an exceed- 

 ingly dangerous saprophytic species 

 only rarely found wild in woods, but 

 attacking and destroying the timber 

 of damp houses, especially coniferous 

 wood. The mycelium of this fungus 

 forms large, white, felted masses 

 with firmer branched strands which 

 serve to conduct water and food 

 substances. The hyphae have clamp 

 connections. It gives rise to out- 

 spread, irregularly -shaped, pitted 

 fructifications of an ochre or rusty- 

 brown colour, and covered with a 

 hymenial layer. Good ventilation 

 of the infected space and dryness 



are the best remedial measures. Merulius sill-ester which occurs in woods is a 

 related form. 



5. The Agaricineae, which include the greatest number of species, have stalked 

 fructifications, commonly known as Mushrooms and Toadstools. The under side of 

 the pileus bears a number of radially-disposed lamellae or gills which are covered 

 with the basidia-producing hymenium. In the early stages of their formation the 

 fructifications consist of nearly spherical masses of interwoven hyphae, in which 

 the stalk and pileus soon become differentiated. Many Agaricineae develop a 

 so-called VELUM, consisting of a thin membrane of hyphal tissue which extends 

 in young fructifications from the stalk to the margin of the pileus, but is after- 

 wards ruptured, and remains as a ring of tissue encircling the stalk (Fig. 416). 

 In Amanita (Figs. 417-419) the rudiments of the stalk and pileus are at first 

 enclosed in a loosely- woven envelope, the VOLVA. In the course of the further 

 development and elongation of the stalk the volva is ruptured, and its torn 

 remnants form a ring or sheath at the base of the stalk, and in many cases are still 

 traceable in the white scales conspicuous on the surface of the pileus. 



FIG. 417. Amanita muscarid. (i nat. size.) Poisoxocs. 



H 



