CRYPTOGAMS 



369 



been undisturbed, the fructifications which appear in autumn form the so-called fairy 

 rings. These rings may attain a diameter of several metres ; they are formed not 

 only by Hymenomycetes (e.g. Amanita muscaria, Boletus edulis), but also by 

 the Morchellas among the Ascomycetes. A few Hymenomycetes are parasitic, and 

 vegetate in the bark or wood of trees. Of such parasitic forms Armillaria mellea, 

 whose mycelium vegetates between the bark and wood of Conifers, is a familiar 

 example. The profusely branching mycelial hyphaj undergo a remarkable modifica- 

 tion (Fig. 291), and become interwoven into flat, black strands from which fine, 

 hair-like byphae are sent out and penetrate the wood for the absorption of nourish- 

 ment. It is from these strands, known as Ehizomorpha, . that the stalked, capitate 

 fructifications are eventually produced. In addition to the subcortical strands, 



Fig. 291.— Armillaria mellea. Por- Pig. 292. — Exotasidium Vaccina. Transverse section 



tion of a rhizomorpha strand (r) 

 with mature (a) and young (b) 

 fructifications. (After Habtig, 

 from v. Tavel ; $ nat. size.) 



through the periphery of a stem of Vaccinium; ep, 

 epidermis ; p, cortical parenchyma ; m, mycelial hypha? ; 

 &', protruding basidia without sterigmata ; &", with 

 rudimentary sterigmata ; &'", with four spores. (After 

 Woronin, x 620.) 



subterranean mycelial strands are developed which pervade the soil and infect the 

 roots of other trees. The rhizomorphs may also be regarded as a form of sclerotia. 

 C'oprinus stercorarius, another Fungus of this same family growing in cow and horse 

 dung, forms also small, round, black sclerotia. 



The Hymenomycetes are further classified according to the increasing complexity 

 exhibited in the structure of their basidial fructifications. 



1. In a few genera no distinctive fructifications are formed, and the autohasidia 

 spring in irregular groups directly from the mycelium. JExobasidium Vaccinii may 

 be taken as a type of this form. The mycelium of this Fungus, which is widely 

 spread in Europe, is parasitic in the Ericaceae, especially on species of Vaccinium ; it 

 causes hypertrophy of the infected parts. The basidia are formed in groups under 

 the epidermis, which they finally rupture (Fig. 292). In this genus, as in many 

 others, accessory fructifications are developed, and as spindle-shaped conidia are 

 abstricted before the formation of the basidia from the mycelium on the surface of 

 the host-plant. 



2 B 



