SECT. I 



CRYPTOGAMS 



409 



in the humus soil of forests, in decaying wood or on dying tree trunks, and 

 produce fructifications, commonly known as toad -stools, protruding from the 

 substratum. The mycelium of the forms vegetating in the soil spreads farther 

 and farther, and dying in the centre as it exhausts the food material of the 

 substratum, occupies continually widening concentric zones. In consequence of 

 this mode of growth, where the development 'has been undisturbed, the fructifi- 

 cations, which appear in autumn, form the so-called fairy rings. A few Hymeno- 

 mycetes 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 and other trees, is a familiar example. The profusely branching mycelial 

 hyphae (Fig. 354) become interwoven into flat, black strands from which tine, hair- 



Fio. 354. -\nnilliii-iii mi'Ui'u. Por- 

 tion of a rhizomorph strand (>) 

 with mature (n) and youn<; (') 

 fructifications. (After HARTIO, 

 from v. TAVEL ; \ nut. si/.-.) 



like hyphte are sent out and penetrate the wood for the absorption of nourishment. 

 It is from these sub-cortical strands, known as IIHIZOMORPHA, that the stalked, 

 capitate fructifications are eventually produced. In addition to the subcortical 

 strands, subterranean rhizomorphs are developed which pervade the soil and 

 infect the roots of other trees. The rhizomorphs may l>c regarded as a form of 

 sclerotia. This fungus is one of those that give rise to photogenic substances 

 which cause the phosphorescence of the infected wood ( 79 ). 



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 basidia 

 spring in irregular groups directly from the mycelium. Exobasidium l"accinn 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. :j ;>"). In this genus, as in 



