238 BRYOPHYTA. [CH. 



Such possible sources of error should be prominently kept in 

 view when we are considering the value of negative evidence 

 as regards the geological history of the Musci. 



A recent writer^ on mosses has expressed the opinion that 

 no doubt the Musci played an exceedingly important r61e in 

 past time. Although we have no proof that this was so, yet 

 it is far from improbable, and the absence of fossil mosses must 

 no doubt be attributed in part to their failure to be preserved 

 in a fossil state. 



In the numerous samples of Coal-Measure vegetation pre- 

 served in extraordinary perfection in the calcareous nodules 

 of England, no certain trace of a moss has so far been 

 discovered. The most delicate tissue in the larger Palaeozoic 

 plants has often been preserved, and in view of such possibilities 

 of petrifaction it might appear strange that if moss-like plants 

 existed no fragments had been preserved. Their absence is, 

 however, no proof of the non-existence of Palaeozoic mosses, 

 but it is a fact which certainly tends towards the assumption 

 that mosses were probably not very abundant in the Coal 

 Period forests. Epiphytic mosses frequently occur on the 

 stems and leaves of ferns and other plants in tropical forests. 

 Such small and comparatively delicate plants would, however, 

 be easily rubbed off or destroyed in the process of fossilisation, 

 and it is extremely rare to find among petrified Palaeozoic 

 plants the external features well preserved. It is probable 

 that the forests extended over low lying and swampy regions, 

 and that, in part, the trees were rooted in a submerged surface. 

 Under such conditions of growth there would not be the same 

 abundance of Bryophytes as in most of our modern forests. 



To whatever cause the absence of mosses may be best 

 attributed, it is a fact that should not be too strongly empha- 

 sised in discussions on plant-evolution. 



Muscites. 



This comprehensive genus may be defined as follows : — 

 Stem filiform, simple or branched, bearing small sessile 



1 Limpricht (90) p. 67. 



