3 2 <5 
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 shrubs 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 
undetermined. The assimilation of organic nitrogenous sub- 
stances is undoubtedly made less difficult on account of the 
number of saprophytic 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 C0 2 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 substratum, 
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 temperature, humidity and wind, yet these 
factors are much more uniform than are the amounts of available 
water supply. The limitations of this paper do not permit going 
into greater detail in respect to the nature and the degree of 
toxicity in bogs, or in respect to the kinds of plants or the parts of 
plants which are most affected. 
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 transformation products of 
