38 BOTANICAL GAZETTE [JANUARY 



turbed, we find the swamp flora, or mixtures of swamp and bog 

 species. 



The nature of the bog plant societies of the Huron basin is shown 

 by the description of several local bogs, selected to show both the 

 local bog flora and the variation in societies, and arranged to present 

 the genetic changes in a bog flora as a basin filled by peat accumu- 

 lation. It is shown that during the early stages of bog development, 

 bog sedge, bog shrub, and conifer societies follow each other in the 

 invasion of the basin. These several societies may vary considerably 

 in composition, but they are closely related and show every gradation 

 in a definite order of succession. The bog conifers, however, show 

 no relationship to the surrounding broad-leaved forests of the upland. 

 On the other hand, where clearing has occurred, swamp sedges, 

 swamp shrubs, and swamp trees gain the ascendency, and these not 

 only show an order of succession among themselves, but are genetically 

 related to the broad-leaved trees of the region. The bog societies 

 are part of the northeastern conifer forest formation, while the swamp 

 societies are related to the southeastern broad-leaved forests. 



An anatomical study of the bog plants shows that epidermal and 

 hypodermal tissues are thick-walled, that a heavy cuticle is present, 

 frequently supplemented by wax and hairs. Resinous bodies are 

 to be found in the roots and leaves of many of the plants. The leaves 

 are usually small and re volute-margined. Palisade tissue makes 

 up a large part of the mesophyll. Mycorhizas are present in most 

 of the plants. Bog plants resemble the plants of dry sand plains 

 in reduction of foliage area, in development of protective coverings 

 for above-ground parts, and in palisade tissues, but differ from the 

 latter in the matter of root development and root structures. 



Experiments indicate that the local bog water itself has no tendency 

 toward the production of xerophilous modifications. Low soil 

 temperatures and lack of soil aeration, however, cause a reduction 

 in the development of the several plant organs. When these two 

 factors are combined, the effect is very marked. 



Experiments with Rumex acetosella are of especial interest in 

 that nearly all of the characteristics of bog plants may be developed 

 either by lowering the soil temperature, as compared with the air 

 temperature, by preventing proper soil aeration, or by growing in 



