THE FUNGI : ASCOMYCETES AND BASIDIOMYCETES 337 



Many studies have been made of the Fungi which occur on dung, and a 

 whole volume might be written upon the dung flora. If samples of dung are 

 kept moist and warm a succession of Fungi will appear, and generally it is 

 found that the same species occur on a sample of a particular dung and 

 generally in the same order. First, various IVIucoraceae make their appear- 

 ance, to be followed by various small Pezizaceae, and later by certain 

 Agaricaceae, particularly species of Coprinus. 



Dead leaves, too, have their own characteristic fungal flora. Many of 

 them are soil Fungi, but some appear to have reached the leaves before they 

 were shed. It is interesting to note in this connection that the number of 

 species occuring on Oak leaves is much larger than those which occur on 

 Beech ; a point which may explain the relatively rapid decomposition of 

 fallen Oak leaves as compared with those of the Beech. 



When we turn to the distribution of the larger species, we find that other 

 factors besides the Fungus itself play a part, for it has already been pointed 

 out that the distribution of many of the Agaricaceae is determined by the 

 mycorrhizal association between the mycelium of the Fungus and the roots 

 of certain plants. In this respect many Fungi appear to be fairly promiscuous, 

 while others are specific as regards their host plant. It follows, therefore, 

 that the distribution of the higher Fungi is to a considerable extent dependent 

 upon that of the phanerogamic vegetation with which they live. Later we 

 shall discuss this question of plant distribution again in some detail, and 

 it will suffice here for us to note a few general points about fungal 

 distribution. 



It has been found that the Fungus flora of woodlands fall into two distinct 

 groups, that which inhabits deciduous woods and that which occurs in 

 coniferous woodlands. For example, TricJioloma virgatum is common in 

 Beech woods, while in coniferous woods it is replaced by TricJioloma terreum. 

 Pastures and heaths also have their own Fungus flora, as any countryman 

 knows who goes in search of the common mushroom. Even sand dunes 

 have their own particular species, one, Inocybe maritima (Fig. 331), living 

 in symbiotic association with the underground stems of the Marram 

 Grass. 



Certain Fungi choose particular localities in which to grow because of 

 some mineral substance which they require. We have pointed out that 

 Pyronevia confiuens, is mainly restricted to burnt ground, while it is recorded 

 that after the disastrous earthquake and fire in Tokyo in 1923, within three 

 days of the fire being put out large areas became covered by another similar 

 Fungus, the orange-coloured Neurospora sitophila. 



Many trees have their own particular flora of micro-fungi, quite apart 

 from those species which are obligate parasites upon them, while other 

 Fungi live exclusively upon one type of decaying material. 



We will defer until Volume IV entering into the complex questions of 



the relationships which exist between parasitic Fungi and their hosts. 



Obviously they vary greatly in difl^erent cases. Some Fungi are widely 



distributed over a varied range of host plants, others are more limited in their 



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