A YORKSHIRE NATURALIST 159 



not been able to make more progress with this inquiry; 

 but regarding the study of the organisation of the 

 carboniferous plants as my more important task, 

 coal has been set aside whenever the other became 

 urgent. Still I don't despair of carrying the black 

 investigation yet a little further. 



The broad conclusions at which I have arrived are 

 not unimportant. In the first place, coals vary enor- 

 mously as to the amount of perforated tissues 

 (mineral charcoal) that they contain. Those of 

 South Wales and Belgium are almost undistinguish- 

 able from this point of view. In some of them half 

 the substance of the coal consists of these fragments 

 of mineral charcoal. Where such is the case, the 

 spores, which are usually of two kinds, macrospores 

 and microspores, are very scanty. Thus, in the 

 Belgian coals that I have already examined, macro- 

 spores are absolutely non-existent, and microspores 

 almost equally so. On the other hand, the perfo- 

 rated tissues are largely of two types, viz., those 

 where the perforations are more or less circular, 

 and those in which the apertures are what are known 

 as " bordered pits." 



The extraordinary fact is, that considering how 

 many of the trees of the carboniferous forests 

 were lepidodendroid and sigillarian, we should have 

 expected that their contributions to the stock of 

 mineral charcoal would have been conspicuous from 

 its amount, but, on the contrary, the real scalariform 

 vascular tissue which is the characteristic form seen 



