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The categories glycophyte, intolerant halophyte, faculta- tive halophyte, and obligate halophyte were defined in relative terms. An obligate halophyte was defined as a plant with optimal growth at moderate or high salinity and incapable of growth at low salinity. A selective literature review summarized field and laboratory evidence con- cerning salt-tolerance limits for marine angiosperms, mangroves, and plants of coastal strand, salt desert, and salt marsh. Extensive field observations, corroborated by several workers, were considered very strong, but not conclusive, evidence in defining tolerance limits of species. Even from field observations, however, very few species appeared to be restricted to salinities above 0.5%. Laboratory techniques were not consistent and seldom approximated natural conditions. Neverthe- less, no laboratory-based evidence was found which definitely showed any angiosperm to be an obligate halophyte, although some were shown to be facultative. Ability to reproduce, rather than short-term growth, Reviews by Uphof (1941), Chapman (1960), and Bernstein (1962) cover aspects of geographic distribution, taxonomic relationships, ecol- ogy, and physiology of halophytes. This paper examines only the litera- ture dealing with the range of salt tolerance of angiosperms from several habitats. The term halophyte, alone or coupled with a number of modifiers, has been defined in several contradictory ways. Some of these defini- tions will be reviewed here, and a single set of terms and definitions to be used as a basis for the rest of the paper will be presented. Schimper (1903) defined a halophyte as a plant which lived normally in saline habitats, but which could ". . . thrive on ordinary soil, for instance on garden-soil, without any addition of common salt." Schimper did not define a saline habitat, but his discussion implied it to be one with more than 2% NaCl. Warming (1909) similarly avoided implying that halophytes were restricted to saline habitats. Stocker (1928) defined halophyte and saline habitat more precisely: a normal glycophyte (non-halophyte) is able to tolerate up to 0.5% NaCl and a halophyte is able to tolerate, at any stage of its life, a salt concentration greater than 0.5%.

It has been long known that certain marine fishes enter fresh-water in addition to anadromous species that run up rivers to spawn. Gunther (1880, p. 202) said: "Almost every large river offers instances of truly marine fishes . . . ascending for hundreds of miles of their course; and not periodically,, or from any apparent physiological necessity, but sporadically throughout the year . . ." Ordinary faunistic surveys, which are usually made without salinity determinations, indicate that this phenomenon is more common in the tropics than in temperate regions. Nevertheless, it is common in North America and several authors have mentioned it. Marine fishes are found in the Atchafalaya River of Louisiana over 160 miles from the sea (Gunter, 1938b) and numerous marine species occur in fresh-water at Homasassa Springs, Florida (Gunter, 1942, Herald and Strickland, 1949). Bailey, Winn and Smith (1954) qttestioned these records but furnished others for the Gulf Coast. Odum (1953) has shown that the fresh-waters of Florida generally, including Homosassa Springs are quite high in salt content. Crabs (Gunter, 1938b) and other marine animals also enter fresh-water, but the action is much more common to fishes and doubtless takes place at all coastal river mouths to some extent. Some fresh-water fishes also descend the rivers and spend a time at sea. Myers (1938, 1949) has proposed a six division classification of fishes with regard to salt tolerance, which is particularly useful in zoogeographic studies. In this paper we are not particularly concerned with those problems. Remarks and records in the literature on the salinity where fishes are captured are scattered, incomplete and hard to find because they are included as side issues in papers devoted to other subjects. The writer attempted to summarize the information for North and Middle America by compiling a list of the fishes of the continent which have been found in both freshwater and sea water (Gunter, 1942). Due to the incompleteness of the literature, the help of a number of ichthyological workers was solicited. The response was gratifying and several unrecorded observations were brought to light. This paper is essentially a revision and extension of the former list. An animal which will withstand or tolerate gross salinity changes is said to be euryhalin. There are all degrees of euryhalinity, grading from animals which can withstand little or no salinity change to those which can change from sea water to fresh-water or vice versa and live in either environment indefinitely. There are also degrees of rapidity withwhich animals can undergo salinity changes, but little is known of this aspect of the subject. The term euryhalin has never been rigidly defined and any rigid definition is essentially arbitrary. The writer (Gunter, op. cit.) defined an euryhalin

Observations are presented of the effects of winter water conditions on the survival, behavior and color patterns of 15 species of marine fishes, comprising 11 families and 80 specimens held in aquaria with continuous flowing water. Only weakfish were found to float when dead, all others remained on the bottom of the test aquaria. The behavior patterns exhibited prior to death were as varied as the species studied. These observations may help to explain aggregations of dead fishes that are often detected accidentally during winter sampling. The largest kill of the study specimens occurred during the 15-20 December, 1962, cold snap. Field observations froin Georgia to Texas reported kills of several of the same species. Schwartz (1963) pointed out the need for observations on the effects of low temperature waters on the behavior and survival of marine fishes as a prelude to speculations regarding natural calamities. This paper gives further observations and presents data on 15 species of marine fishes, comprising tt families and 80 specimens, which were subjected to natural winter water temperatures and salinities. Specimens were obtained from pound nets near the mouth of the Potomac River, Smith Point, Virginia, on 25 September, 1962. A boat, equipped with two circular tanks, six feet in diameter and three feet deep, which were supplied with Chesapeake Bay surface water, was used to transport the fish the 20 miles to the Chesapeake Biological Laboratory. Temperature and salinity conditions at the time of capture at Smith Point were 20.7 C and 19.5 ppt. The fish were transferred into four-foot-square indoor aquaria, with unfiltered, flowing water (20.2 C and 16.1 ppt) pumped from the Patuxent River, Solomons, Maryland. Distribution of the fish in the aquaria was as follows: Tank 1, cownose ray, southern stingray and sharksucker; Tank 2, kingfish, croaker, red drum and stargazer; Tank 3, spot, filefish, striped burrfish and weakfish; Tank 4, black sea bass, spot (small), searobin and swellfish; and Tank 5, toadfish. Beaven (1960) reported the general salinity and temperature conditions observed at Solomnons over a 20-year period. Salinities during the observation period and their relationship to 25-year averages are illustrated in Figure t. The oxygen conditions of the water in the aquaria were always more than adequate for fish survival. Generally, the fall and winter of 1962-63 was colder than usual. The Chesapeake Bay to Point Lookout was frozen completely over on 18 February, 1963, for the first time since 1934. Ice, 6-10 inches thick, prevailed from the head of the Bay to James Island (62 nautical miles). A one-quarter to one-inch thickness of ice covered the Bay southward another 20 nautical miles to Point Lookout. 1 Contr. No. 246. Natural Resources Institute of the University of Maryland, Solomons, Maryland.

The relation of coastal fishes to salinity of the environment is one of the most important aspects of their natural history. The whole problem, because of its connections with physiology and ecology, has bearing on one of the oldest and most important steps of biological evolution, the migration of animals from sea to land. In this paper one aspect of this many-sided problem is examined, by taking the step of compiling a list of fishes of the continent of North and Middle America that have been found in both freshwater and