THE DECIDUOUS FOREST CLIMAX. 199 



The vegetation is considered under the (1) border zone of Decodon and 

 Typha, and the maple-alder zone of Acer, Alnus, Prunus, and Rhus. The 

 central zone of the island consists of Vaccinium and Sphagnum, with Rhyn- 

 chospora, Heleocharis, Aspidium, Dulichium, etc., in the various stages of 

 development. The same author (1912) has also studied the development of 

 vegetation in the lakes and swamps of Ohio, recognizing the major stages and 

 the various associations concerned in the primary successions from open water 

 to the final vegetation, and dealing briefly with the secondary successions 

 arising in consequence of fire, drainage, and cultivation. The primary suc- 

 cession is divided into the following stages: (1) open water, (2) marginal, 

 (3) shore, (4) bog, (5) mesophytic. Each of these is termed a succession, but 

 this is evidently a lapse, since the author points out clearly that they are stages 

 of one great succession. In the open water are found plankton associations. 

 The marginal stage is represented by: (1) submerged associations and floating 

 associations {Chora, Ceratophyllum, Pdamogeton, etc.) ; (2) semi-aquatic asso- 

 ciations (Castalia, Nymphaea, and Polygonum); (3) floating associations 

 (Lemna, Spirodeld). The shore stage consists of the following associations: 

 (1) Decodon vertidllatv^; (2) Carex-Juncus-Sdrpus; (3) Typha; (4) Calama- 

 grostis canadensis; (5) Phragmites communis. The bog stage of development 

 is represented by: (1) bog-meadow associations, (a) Vacdnium^Sphagnum, 

 (6) Carex-Juncus; (2) bog-heath, (o) Chamaedaphne, (6) Potentilla frviicosa, 

 (c) Gaylussacior-Vacdnium; (3) bog-shrub, (a) Alnus-Rhus, (b) Salix-Popvlus, 

 (c) CephaJanthus-Cofrnus; (4) bog-forest, (o) Larix, (6) Thuja. The meso- 

 phytic forest is represented typically by the Acer-Fraxinus-Ulmus association. 



Dachnowski (1912) in his complete and thoroughgoing monograph of Ohio 

 peat-bogs, has described the succession in detail, and has reached the following 

 conclusions with regard to the factors and reactions concerned : 



The persistence of winter cold and ice through the summer is not proved 

 either by observation or by recording instruments. Mesophytic invaders are 

 not killed by low temperature, but by physiological drouth which decreases 

 absorption at a time when transpiration and growth are making maximum 

 demands. Distribution within the bog is also explained by the same factor. 

 Many swamp and muck soils exhibit a sterility not remedied by drainage or 

 fertiUzers. The sterihty seems most marked where a greater amount and 

 activity of bog toxins are indicated. In untreated bog-water, many colored 

 substances are deposited upon the roots of wheat plants as a result of the 

 oxidizing action of the roots. The general decay of root-tips indicates that 

 the oxidizing activity is insufficient to decrease the harmful effects of bog 

 toxins. It is possible that the ecesis, association, and succession of plants 

 depend primanly upon respiration, and that bog-plants differ from other 

 plants in respiration. The author beUeves that his results warrant the con- 

 clusion that bog-water and soils contain toxins which are the cause of xero- 

 morphy in bog-plants, and of decreased f ertihty of the soil itself. 



Organic substances in peat soils, while inhibiting cultivated plants, have 

 little or no effect on xeromorphic plants. They may be positive forces not 

 only in producing succession in bogs, but also in determining xeromorphy. 

 Such substances are decisive even when the amoimt of air and water in the 

 soil is abundant, and temperature and humidity are favorable to growth. 

 Peat soils are very rich in bacteria with a wide range of activity. They vary in 

 kind and number with the nature of the substratum. The products of bac- 

 terial activity constitute unsanitary conditions in the soil, limit ing the rate 

 with which organic compounds are broken down into ammonia. The r61e of 

 the bacteria indicates a considerable relation between the processes of organic 

 decomposition and the succession in bogs and marshes. 



