. The plant societies of Chicago and its vicinity. Plant ecology; Botany; Botany. 3° THE PLANT SOCIETIES OF (Blue grass) and Agrostis alba vulgaris (Red top), there are often other plants in abundance, e. g., Thalictrum purpurascens (Meadow rue), Fra- garia Virginia?ia (Strawberry), and Anemone Pennsylvanica. The eco- logical meaning of the meadow is not clear. Probably mowing or grazing is responsible for the failure of a mesophytic forest to Fig. 15.—Terrace in the flood plain of tlie Des Plaines river at Glendon Parle, showing how a mesophytic flood plain may become xerophytic. Th
. The plant societies of Chicago and its vicinity. Plant ecology; Botany; Botany. 3° THE PLANT SOCIETIES OF (Blue grass) and Agrostis alba vulgaris (Red top), there are often other plants in abundance, e. g., Thalictrum purpurascens (Meadow rue), Fra- garia Virginia?ia (Strawberry), and Anemone Pennsylvanica. The eco- logical meaning of the meadow is not clear. Probably mowing or grazing is responsible for the failure of a mesophytic forest to Fig. 15.—Terrace in the flood plain of tlie Des Plaines river at Glendon Parle, showing how a mesophytic flood plain may become xerophytic. The opposite bank shows deposition and flood plain enlargement {fi^, ii). Extensive thorn (Crataegus) thickets sometimes occur in these meadows, and probably betoken the beginning of a mesophytic forest. E.\ten- sive and apparently natural meadows are found in the Calumet valley. As we have seen, the climax type of vegetation on the flood plain is the mesophytic forest; but here, as well as on the river bluffs, the climax may be but temporary. Retrogression is almost sure to come in connection with terrace formation. While it is true that deposition is the main feature of flood plains, it is also true that erosion has not ceased; the downward cutting of the river once more causes vertical banks, though this time in its own flood plain. This action is seen in fig. 14, which shows the beginning of the new erosive phase, and its indication in the falling elm. There has doubtless been lateral erosion here also, since elms are not usually marginal trees. Mg. /j shows. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Cowles, Henry Chandler, 1869-1939. Chicago, The Geographic Society of Chicago
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