12 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
termediate between the floating water plants and the amphibious vegeta- 
tion; they root in the mud from 1 3^ to 3 meters below the surface of the 
water. Here also several forerunners are growing of Pontederia cordata L. 
Taking these pure aquatic plants as a whole, there are relatively few species 
in comparison with the amphibious and semi-amphibious species along the 
edges of the lakes. . 
The margins of the ponds and lakes are surrounded by a great number 
of different species of amphibious plants; sometimes they form pure associa- 
tions, but mostly they occur in societies of different species. From a 
depth of 3^ to I meter the lakes are thickly covered with Scirpus lacustris L., 
S. fltiviatilis (Torr.) Gray (rare), Typha latifolia L., Phragmites communis 
L., Sagittaria lancifolia L., S. graminea Michx., Acorus Calamus L., Zizania 
palustris L., Glyceria fluitans (L.) R. Br. (also sometimes between the water 
lilies), G. nervata (Willd.) Trin., Dulichium arundinaceum (L.) Britton 
(rare), Iris fulva Ker, and I.hexagona Walt. In less pure associations are 
to be seen Alisma Plantago L., Sparganium eurycarpum Engelm., S. lucidum 
Fern. & Fames; Nelumbo lutea also often grows here, although in few 
individuals. A very interesting species growing in ponds, borders of lakes, 
and even on mud flats, is Thalia dealhata Roscoe, a member of the Maran- 
taceae which reaches here in this region one of its northern limits. Fre- 
quently it is associated with the beautiful flowering Hymenocallis occidentalis 
(Le Conte) Kunth. Mud flats and shallow ponds are for several miles 
covered with Polygonum Muhlenbergii (Meisn.) Wats., hardly showing any 
other species in their association ; their rootstocks are very deeply imbedded 
in the mud. Also Cicuta maculata L., Saururus cernuus L., and Jussiaea 
diffusa Forst. are growing amongst such mud plants. When the mud flats 
become partly dry in summer there may be for a time a vegetation of any 
species whose seeds happen to drop and to germinate there, but these always 
disappear when the land becomes inundated again. To such species belong 
Polygonum Hydropiper L., Solanum carolinense L., Humulus alatus Ait., 
Lippia lanceolata Michx., Rotala ramosior (L.) Koehne, and a few others. 
When such mud flats happen to remain dry, these and other species cover 
the surface entirely; then a struggle for life soon eradicates some of the 
least resistant individuals, and eventually entire species. 
Other amphibious plants along the margins of lakes are Equisetum 
hyemale L., Cicuta maculata L., Sium cicutaefolium Schrank, Rumex crispus 
L., R. verticillatus L., Jussiaea diffusa Forst., Bacopa rotundifolia (Michx.) 
Wettst., Senecio aureus L., Carex monile Tuckerm., C. conjuncta Boott, 
Mimulus ringens L., Stachys palustris L., Diodia virginiana I.., Ranunculus 
abortivus L., Ludvigia palustris (L.) Ell., Lobelia siphilitica L., L. cardinalis 
L., Nasturtium palustre L., and (in large tracts) Hibiscus lasiocarpus Cav. 
Very large areas of swamps are covered with Taxodium distichum (L.) 
Richard and Nyssa aquatica L. Gigantic trees of the former as well of the 
latter form pure stands or grow mixed near one another covering several 
square kilometers in extent. The Taxodium forest has only few associates 
