— 90 — 
Brachythecium salebrosum [Hoffm.] Bryol. Eur. 
Dicranella heteromalla [Dill.] Schimp. 
Entodon cladorrhizans (Hedw.) C. M. 
Tetraphis pellucida [L.] Hedw. ( Georgia pellucida Rabenh.) 
Mnium cuspidatum L., Hedw. 
Platygyrium repens [Brid.] Bryol. Eur.* 
Rhynchostegium serrulatum (Hedw.) Jaeg.* 
Stereodon imponens (Hedw.) Lindb. 
Stereodon Haldanianus (Grev.) Lindb. 
Thuidium delicatulum [L.] Mitt.* 
Thuidium minutulum [Hedw.] Bryol. Eur. 
D. Loose sandstone blocks on shaded slope. 
Hedwigia ciliata Ehrh., Bryol. Eur. (H. albicans Lindb.) 
Dianthera Association. Water Willow Association. 
6. The forest of the flood-plains of the rivers and larger tributaries is the 
result of a succession of ecological groups which can still be made out to a large 
extent from scattered remnants. This succession may best start with a sand- 
bar or a bit of shallowly submerged bank. If for any reason the water becomes 
shallow beyond a certain limit the Water Willow takes possession and the vege- 
tational succession then starts with the Dianthera Association. Some of the 
aquatic mosses might be expected here, but none have been reported from this 
association thus far. The Dianthera acts as an obstacle to slow down the water 
currents, thus leading to a greater deposition of sand and silt at that point, as 
well as directly stopping much moving material. In this way the water becomes 
successively more shallow and eventually conditions become suitable for the 
sprouting and rooting of other plants which will take possession of the habitat 
in place of the disappearing Dianthera. The plant group following the Dian- 
thera may be known as follows: 
7. Platanus-Salix Association. Sycamore- Willow Forest. 
This association is rarely of any great extent and probably very rarely lasts 
more than one generation of willows, excepting at the edge of a rather permanent 
bank, where subject to severe floods. Ordinarily the level of the soil raises to 
some extent with the development of the plants and conditions then speedily 
become suitable for the next following association. The following mosses are to 
be counted as members of this association, more particularly along the sandy 
banks of the tributaries of the larger rivers: 
Aphanorhegma serratum (Hook. & Wils.) Sull. 
Physcomitrium immersum (Rich.) C. M. 
Pogonatum pennsylvanicum (Hedw.) Paris. (P. brevicaule Beauv.) 
8. Acer saccharinum—Ulmus americana Association. Silver Maple— White Elm 
Forest. 
This forest, with a large number of other trees besides the Silver Maple 
and White Elm, seems to be the prevailing type in the few scattering remnants 
