326 The Ohio Naturalist. [Vol. XI, No. 6, 



mineral nutrients, but by an excessive, defective or preventive 

 action in the substratum. The lack of mineral constituents such 

 as lime, potash, and phosphoric acid does not even render it 

 difficult for mesophytic shrtibs and trees to invade and grow as 

 the deposit is built up and oxidation processes become prominent 

 in the surface layer of the substratum. To what extent bog 

 plants require the organic compounds arising in peat soils is still 

 undetennined. The assimilation of organic nitrogenous sub- 

 stances is undoubtedly made less difficult on account of the 

 number of saprophj'tic fungi and the endotrophic mycorhiza 

 usually present. 



The characteristic foliage of bog plants is distinctly an 

 effect to a habitat with a moderate or scanty physiological 

 soil-water content. Extreme xeromorphy is reached in the 

 upper layer of open shrub associations; here the CO2 percent- 

 age of the vertical gradient is least and approximates that of 

 the free air; the combined effect of the intensity of light and the 

 greater saturation deficiency of the air is provided for by an 

 increased thickness of the mesophyll layer in the foliage to min- 

 imize disturbances in the carbon dioxide supply. This and the 

 narrow leaves with restricted stomata confined to deep furrows 

 and in some cases protected by hairs, wax, or heavy cuticle, are 

 devices common to plants in bogs where the plants must protect 

 themselves against unfavorable water content in the substratmn, 

 and not against unfavorable atmospheric influences. The aerial 

 parts of plants are constantly losing water by transpiration, a 

 process similar to evaporation but controlled by the plants within 

 certain limits. To re-establish equilibrium this water loss is 

 replaced by the supply of water from the substratum by root 

 absorption. The taller plants are thus subjected to a difficulty 

 in maintaining the balance between absorption and transpiration 

 in the same manner as are plants living in deserts or in sandy 

 regions. Though the amount of transpiration exhibited by 

 plants is partly influenced by the physical conditions of the 

 atmosphere such as tem]jerature, humidity and wind, yet these 

 factors are much more unifonn than are the amounts of available 

 water supply. The limitations of this paper do not pemiit going 

 into greater detail in respect to the nature arid the degree of 

 toxicity in bogs, or in respect to the kinds of plants or the parts of 

 plants which are most afl^ected. 



The nearest analogue of the accumulation and the conditions 

 of growth for the vegetation of the coal measures are the bogs 

 and marshes of today. Were there no other trustworthy records 

 of the occurrence of bacteria and fungi in Palaeozic times (22), it 

 would still be a natural supposition that these organisms were 

 abundantly represented, and produced physical and chemical 

 changes in the substratum. The transfonnation products of 



