SUCCESSIONS IN BOGS 39 



ecology of fossil plants, in particular the physical conditions under 

 which the plants of the coal-measure grew, and the succession of 

 plant associations within the same ancient swamp area. The pres- 

 ence in the petrified debris, of fungi, mycorrhiza, woody pneu- 

 motophores (Stigmaria) ; the change in color of nodules taken 

 from the bottom to the top of a seam, and the differences in the 

 plant-remains, strongly suggest unfavorable conditions in the 

 peaty substratum. It is not necessary, therefore, to postulate 

 a moist tropical climate with vapors heavily charged with carbon 

 dioxide. 



