WATER AND SWAMP FLORA. 49 
by the rosettes of their floating leaves, as in sundew (Drosera inter- 
media), water feather (Hottonia inflata), bladderwort (Utricularia 
inflata), or by leaf-covered stems, as in hornwort (Ceratophyllum). 
LITHOPHYTIC AND LIMNAAN CLASSES. 
Of submersed hydrophytes rooting on the solid rocky bed of swiftly 
running brooks two species of Podostemon occur in the mountainous 
regions. They are moss-like plants, their roots provided with peculiar 
organs by the aid of which they fasten themselves closely to the rocks. 
More numerous species of different families constitute that association 
of submersed hydrophytes which take root in the soft soil (Limnean 
associations). These are in some cases provided, in addition to the 
immersed foliage, with peculiarly constructed shield-like leaves floating 
on the surface, only their flowers being lifted above the water, of 
which the following are examples: 
Castalia (water lily) . Sagittaria natans (arrow leaf). 
Nelumbo (water chinquapin). Potamogeton spp. (pondweeds) . 
Nymphaea (spatter-dock) . Callitriche heterophylla (water star) . 
Limnanthemum lacunosum (floating heart) . 
Others have the foliage entirely suomersed and of one form, as 
water crowfoot (Batrachium divaricatum), bladderworts ( Utricularia 
vulgaris and U. purpurea), water milfoils (Myreophyllum spp.), with 
their leaves finely divided; Vallisneria, with long strap-shaped leaves, 
and numerous pondweeds (Heteranthera, Vajas spp., Philotria, Zanni- 
chellia, and Ruppia), with the leaves from narrowly lanceolate to linear. 
These Limnezan aquatics, with their stems mostly emerging from the 
water at flowering, but their seeds ripening beneath it, form the fre- 
quently very dense vegetation of ponds, lakes, and semistagnant 
waters of the estuaries. Of this association, the species are especially 
numerous in the Coast plain. 
PALUSTRIAN CLASSES. 
This association embraces the halophytes and fresh-water plants 
which root in a water-soaked soil, with their leaves and flowering 
stems above, and frequently their bases alone surrounded by water. 
They are nearly all perennials, with stout roots or strong running root- 
stocks (rhizomas), and cover the extensive open marshes of the tide- 
water regions and river alluvium. Large monocotyledonous plants of 
various kinds form the characteristic feature of this vegetation, of 
which the following are representatives: 
Phragmites (tall reed). Scirpus spp. (bulrush) . 
Spartina spp. (cord grass). Cladium effusum (saw grass) . 
Zizania, Zizianopsis (water rice). Scirpus maritimus (triangular-stemmed 
Typha spp. (cattail) . bulrush). 
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