514 BOTANICAL GAZETTE [December 



4. Some plants in contact with peat soil solutions may cause 

 the organic constituents to be precipitated in an insoluble form. 



5. In other plants the different organic carbon and nitrogen 

 compounds arising in peat through the activity of microorganisms 

 may be absorbed and assimilated. The chemical formula and 

 transpiration data alone afford no indication of the physiological 

 importance of the substances, hence the nutritive value of these 

 compounds should be estimated on the basis of the total water 

 requirement of a plant during its period of growth and the ratio 

 between carbon, nitrogen, and ash in the plant. 



6. The phenomena of absorption and tolerance of plants in bogs 

 deal plainly not with osmotic pressure relations so much as with 

 considerations of the permeability of the absorbing protoplasmic 

 membrane, its power of endurance, and its ability by enzymic 

 action either to absorb and assimilate or to transform injurious 

 bodies into insoluble, impermeable compounds. 



7. The organic disintegration substances in peat soils, while 

 inhibitory to agricultural plants, have little or no effect upon 

 certain xerophytic plants. It is concluded, therefore, that they 

 may be positive forces not only in producing the natural succes- 

 sion of vegetation in bogs, but also in determinating xeromorphy 

 and the associated relation of the members, within each group, 

 which best succeed upon peat deposits. These organic substances 

 play the differentiating role and are a cause of the infertility of 

 peat deposits even when the amount of air and water in the soil 

 is abundant and the temperature and humidity conditions are 

 favorable to growth. 



It is needless to point out that these facts have an important 

 bearing on the agricultural exploitation of peat deposits and on 

 the subject of the proper value of peat land to agriculture. 



my thanks to Mr. M. G. Dickey 



and Mr. M. Corotis for their 

 tion data in tables I to III. 



Botanical Laboratory 

 Ohio State University 



