208 THALLOrHYTA. [CH. 



Without going into further details we may very briefly refer 

 to the larger subdivisions of this group of Thallophytes. 



PHYCOMYCETES. Mycelium usually consisting of a single cell. 



noMY^-^T^^^^' Reproduction by means of conidia, and in many 



includino- ' cases also by the conjugation of two similar 



Chytridiaceae, &c. hyphae or by the fertilisation of an egg-cell con- 

 tained in an oogonium. 



MESOMYCETES, ^ , .. , . , ,, -r,. . a 



including the Intermediate between the Phycomycetes and 



Sub-classes the higher fungi. Multicellular hyphae. No 



HEMIASCI and sexual organs. 



HEMIBASIDII. ^ 



MYCOMYCETES. Septate vegetative mycelium. No sexual re- 



includmg the production — as a general rule. Asexual conidia 



ASCOMYCETES and ^^*^ other forms of spores. In the Ascomycetes the 



BASIDIOMYCETES. spores are found in characteristic club-shaped cases 



or asci ; in the Basidiomycetes the spores are borne 



on special branches from swollen cells known as 



hasidia. The sporophore or spore-bearing body 



in this group may attain a considerable size 



(e.g. Agaricus, Poli/porus, &c.) and exhibit a 



distinct internal differentiation. 



Before describing a few examples of fossil fungi, it is 

 important to consider the general question of their manner of 

 occurrence and determination. Considering the small size and 

 delicate nature of most fungi, it is not surprising that we have 

 but few satisfactory records of well-defined fossil forms. The 

 large leathery sporophores of Polyporus and other genera of 

 the Basidiomycetes, which are familiar objects as yellow or brown 

 brackets projecting from the trunks of diseased forest trees, have 

 been found in a fairly perfect condition in the Cambridgeshire 

 peat-beds, and examples have been described also by continental 

 writers \ As a general rule, however, we have to depend on 

 the chance mineralisation or petrifaction of the hyphae of a 

 fungus-mycelium which has invaded the living or dead tissues 

 of some higher plant. In the literature on fossil plants there 

 are numerous recorded species of fungi founded on dark coloured 

 spots and blotches on the impression of a leaf Most of such 

 records are worthless ; the external features being usually too 



1 e.g. Ludwig (57) PI. xvi. fig. 1. 



