94 THE RELATION OF PLANTS TO TIDE-LEVELS 
a principal constituent of the felts over the surface of the mud, among the 
Spartina patens plants, up to 7 feet (e. g., 25 north by 800 east). Along the 
west shore L. estuarw gets up to the 7-foot level among Spartina glabra in 
places where the soil is kept barely damp by seepage of water from the shore 
(1,800 north by 820 west, etc.). On the Sandspit, L. wstuarw is rarely found 
above the 6.5-foot level (500 east), though, as we have seen, it is present just 
below this level. 
Lyngbya lutea is a chief constituent of rather firm felts occurring on wharves 
and beaches of the west shore. It is found in patches of a few square centi- 
meters in area, up as high as the 7-foot level. This species is also present 
sparingly at lower levels down to 3 feet. 
Lyngbya semiplena and several other smaller species are frequently found 
together with L. estuarvi and its associates about the borders of the Marsh, and 
also less frequently on the shore of the Spit. L. semiplena is the most abundant 
and widespread of all the Cyanophycee on the Marsh. Though the smaller 
species have not been identified, their size, color, and other characters were noted 
carefully enough to enable us to determine that they are also widely distributed 
along the lower edge of this belt, as well as just below it. 
Microcoleus chthonoplastes, and less frequently M. tenerrumus, may also 
enter rather sparsely into the make-up of the felts we have mentioned. The 
former species is found widely, though locally, distributed about the whole 
shore of the harbor, chiefly between the 6 and % foot levels. The gelatinous 
matrix of these alex apparently aids in giving substance to the composite felts 
or more gelatinous incrustations. But M. chthonoplastes also occurs on the 
bare mud between stalks of Salicornia or Spartina in nearly pure, irregular, 
olive-green patches, several centimeters across. In these gelatinous patches a 
sparse admixture of one or more species of Lyngbya, of Microcoleus tenerrimus, 
and of an Oscillatoria may sometimes be present, which, however, does not 
destroy the glistening, slimy appearance of these masses. 
Two species of Nostoc were noted near the upper limit of this belt, in the 
neighborhood of fresh-water streams. The smaller species, found at 1,010 
north by 1,060 east at 7 to 7.5 feet, had cells 3 to 3.54 in diameter. It formed 
brownish gelatinous lobules over the mud. ‘The second and larger species, 
found at 560 south by 890 east at 7 to 7.5 feet, had cells 5.54 and heterocysts 
6.54 in diameter. It forms a smooth, brownish coating over the mud. 
Aside from the scattered bits of Oscillatorta just mentioned, alge of this 
genus are not frequent on the mud or pebbles of the shore at this level. Several 
species occur between these levels on piles, wrecks, and on the bell of a hydraulic 
ram at 2,380 north by 1,000 west. 
Polycystis elabens is a minute bluish-green alga, the spherical cells of which 
are aggregated in a gelatinous coat over the mud, among plants of Spartina 
patens, on the Marsh at 7 feet above mean low water. It is quite probable that 
it occurs elsewhere, since it and its associates are so small as to be readily 
overlooked. : 
hivularva is represented by 2 species on the shores in this belt. R. plicata is 
found on the eastern shore near 400 north at 7.5 to 8 feet, on mud among 
clumps of Jris versicolor. The soil here is saturated with fresh water, either 
seeping or trickling from springs a few feet further up the beach. No salt could 
be detected by taste in the sap of root or leaf of plants growing in this soil. Of 
