VIl] POLYPORUS. 221 



compares them with the zygospores of the freshwater algae 

 Desmideae. Hitherto these spore-like fossils have only been 

 recorded as isolated spheres, but in the example shown in 

 fig. 41 F there is a distinct tubular and thin-walled stalk 

 attached to the Zygosporites. The specimen was found in the 

 partially disorganised cortical tissue of a Lyginodendron stem 

 from the English Coal-Measures. It is difficult to decide as to 

 the precise nature of the fossil, but the presence of the hyphal 

 stalk points to a fungus rather than an alga as the most 

 probable type of plant with which to connect it. It may 

 possibly be a sporangium of a fungus comparable with the 

 common mould Mucor, or it may be a zygospore formed by 

 the conjugation of two hyphae of which only one has been 

 preserved. 



For an example of a fossil representative of the Basidiomy- 

 cetes we may turn to the excellent monograph by Conwentz 

 on the Baltic amber trees, and quote one of the forms which he 

 has described. 



Polyporus vaporarius Fr. /. succinea^,fig. 43, 2. In several 

 preparations of the wood preserved by petrifaction in amber 

 Conwentz found distinct indications of the ravages of a fungus, 

 which suggested the presence of the recent species Poly- 

 porus vaporarius Fr. With the help of the indirect evidence 

 afforded by the pathological effects as seen in the tissues of 

 the host-plant, and the direct evidence of the fungal mycelium 

 Conwentz was led to this identification. 



The mycelium is brown in colour, in part thick-walled, and 

 in part with thin walls, transversely septate and not much 

 branched. In the portion of one of Conwentz' figures repro- 

 duced in fig. 43, 2, the rents and holes in the tracheid walls 

 are clearly shown; they afford the indirect evidence of fungal 

 attacks, and are of the same nature as those shown in fig. 42, 

 B, C and E. 



Enough has been said to call attention to the paucity of 

 exact data on which to generalise as to the geological history 



1 Conwentz (90) p. 119, PI. xi. pp. 2, 3, PI. xv. fig. 8. 



