218 THALLOPHYTA. [CH. 



Peronosporeae. In Smith's description the mycelium is de- 

 scribed as bearing spherical swellings containing zoospores. 

 These spherical organs are fairly abundant and not infrequently 

 met with in sections of petrified plant-tissues from the English 

 Coal-Measures ; they may be oogonia or sporangia, or in 

 some cases mere vesicular expansions of a purely vegetative 

 hypha. No confirmation has been given to the supposed spores 

 referred to by Smith. Prof Williamson and others have care- 

 fully examined the specimens, but they have failed to detect 

 any trace of reproductive cells enclosed in the spherical sacs^. 

 The mycelium does not appear to show any satisfactory 

 evidence of its being septate as figured by Smith. 



The example shown in fig. 41 E has been drawn from one 

 of the Williamson specimens : it illustrates the form and 

 manner of occurrence of the characteristic swellings. It is 

 probable that some at least of the vesicles are either sporangia 

 or oogonia, but we cannot speak with absolute confidence as to 

 their precise nature. The general habit and structure of the 

 fungus favour its inclusion in the class of Phycomycetes. The 

 occurrence of several of the vesicles close together on short 

 hyphal branches, as shown in Williamson's figures, suggests the 

 spherical swellings on vegetative hyphae, but it is impossible to 

 speak with absolute confidence. There is a close resemblance 

 between this English form and one recently described by 

 Renault as Palaeomyces gracilis Ren.^; the two fossils should 

 probably be placed in the same genus. 



The examples referred to below and originally recorded by 

 Cash and Hick no doubt belong to the same type as Smith's 

 Peronosporites. 



The sketches reproduced in fig. 44 have been drawn from 

 specimens originally described by Cash and Hick in 1878'. 

 The sections were cut from a calcareous nodule from the 

 Halifax Coal-Measures containing fragments of various plants 

 and among others a piece of cortical tissue, probably of a 

 Lepidodendron or Stigmaria. In a transverse section of this 



i Williamsou (81) PI. xlviii. p. 301. 



2 Eenault (96) p. 439, figs. 88 and 89. 



3 Cash and Hick (78^). 



