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 revolute-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 
