April, 1911.] The Ancient Vegetation of Ohio. 325 



which are briefly as follows: Poorly drained and undraincd 

 water basins and lowlands whether in areas characterized by lime- 

 stone formations, by sandstone, or glacial drift, become physio- 

 logically arid habitats with the accumulation of vegetable debris. 

 Although water is so abundant in bogs and swamps, yet it is 

 largely unavailable to the plants on account of various decom- 

 position products due to the activity of low organisms in the 

 debris-substratum, especially such saprophytes as bacteria and 

 fungi. Peat soils contain bacteria and other fungi in greater 

 number than supposed hitherto, inducing diastatic, inverting, 

 proteolytic, cytohydrolytic and reducing action in the upper 

 layer of the substratum. They vary in kind and number with 

 the nature of the substratum, and show marked interdependence 

 as well as antagonistic action. It has been found that as a gen- 

 eral rule there is an accumulation of injurious substances which 

 must be removed if no deleterious action is to follow, and if com- 

 plete decomposition of the debris is not to be retarded. 



The complex and rather ill-defined "humus acids," more 

 ■Specifically humic, ulmic, crenic, and apocrenic acids, are not 

 the important constituents to which peat owes its antiseptic 

 properties and which interfere with the action of bacterial organ- 

 isms. In Ohio peat deposits, at least, the presence of injurious 

 substances in the substratum is not in direct relation to acidity 

 in the soil. Tests on the reducing powers of peat soils show that 

 the wind driven aeration has httle effect on the peat substratum 

 beneath the two-feet level. A shallow superficial zone of oxida- 

 tion exists in peat soils, and the debris below this is sometimes so 

 charged with injurious decomposition products and gases, and so 

 far unaerated as to be inhospitable to all organisms but anaerobic 

 bacteria. 



In the growing season the temperature of peat soil in the 

 more xerophytic of the succeeding bog associations is not below 

 that of other soils. Rapid and passing changes of air tem- 

 peratures and the occasional extremes do not affect the sub- 

 stratum temperatures. Only average effects prevail and the 

 great periodic changes of the dominant climate. The tempera- 

 tures of the deeper peat strata indicate that there is scarcely 

 anything of a seasonal descent analogous to the circulation or 

 "overturn" in lakes or in ocean. 



The continued growth and persistence of the closely related 

 plant association and the slow succession of vegetation types in a 

 habitat of that character is no longer incomprehensible if we 

 remember that the vegetation grows on top of the accumulating 

 debris and that the water table is always at a high level. The 

 disturbance of the balance produced in the soil is thus not unfavor- 

 able to the dominance of the associations. There occur natural 

 successions which are determined, however, not by a deficiency of 



