330 
A. G. Tansley. 
Other Types of Forest. 
In this neighbourhood the oak-hickory forest ( Quercus alba, 
rubva, velutina, macrocarpa, Carya ovata, Juglans spp., etc.) on the 
clay cliffs was visited—quite a different type from the beech-maple 
climax forest already described. Here, however, the oak-hickory 
forest is regarded as the climax forest, the climatic region in which 
the beech-maple forest is the climax type having now been left. 
The trees on these clay cliffs are never very large or lofty, though 
the forest is mature. 
The V-shaped ravines cut by small streams through these clay 
cliffs present an interesting and decidedly more hygrophytic type of 
vegetation, including such trees as Acer saccliarum, Tilia americana, 
Quercus rubra, Uhnus americana ; and such herbaceous plants as the 
handsome Arabia racemosa, A. nudicaulis, Sanicula marylandica, 
Hepatica acutiloba, Thalictrum dioicum, Solidago latifolia. This 
ravine forest is closely allied to the flood-plain and to the eastern 
climax types. 
Another type of forest visited by the party during their stay at 
Chicago was the flood-plain forest developed along the damp river 
bottoms. This is a very characteristic type and quite rich 
floristically. Salix nigra, S. amygdaloides and Populus deltoides 
frequently fringe the river itself, and in the forest behind Uhnus 
americana, Acer saccliarum and Platanus occidentalis are very 
characteristic, associated with Fraxinus americana and F. nigra, 
Acer Neguudo, Juglans spp. etc. On the ground Osmorhiza brevi- 
stylis, Cryptotcenia canadensis, Convolvulus sepium, Arabia nudicaulis, 
Sicyos angulatus, Campanula americana and many other species 
occur. 
This river-bottom type of forest is specially interesting because 
it is the type which extends, though greatly impoverished floristi¬ 
cally, far to the westward into the region of climatic prairie, 
and indeed along the larger rivers right through the Great Plains 
region to the base of the Rocky Mountains. Psedera ( Ampelopsis ) 
quinquefolia, the “ Virginia creeper,” is ubiquitous in all these types 
of deciduous forest. 
An interesting tamarack ( Larix laricina ) swamp, developed 
just behind the dunes, on the edge of an old river valley was visited 
on August 3rd. Here a succession can be traced from open water 
(perhaps an old hole in the river-bed that remained as a pond 
after the river was obliterated) of which practically nothing remains, 
through reed-swamp and sedge to tamarack wood. The centre of 
