120 THE RELATION OF PLANTS TO TIDE-LEVELS 
appearance in the whole Marsh mark it off as a distinct area. The grass is very 
dense and luxuriant, falling over late in the season into irregular hollows and 
ridges like “ licks ” on the hair of a cow. Its even, light-green color is especially 
pleasing to the eye. At 40 north and 1,050 east it reaches a height of 7 dm., 
6 dm. at 25 north, and 5.2 dm. at 0 north. Outliers of Juncus gerard: extend 
only as far north as 81 south. Here the Spartina is only 3 to 4.5 dm. tall, and 
at 25 south it drops to 2 or 3dm. Aériplex patula hastata, Limonium carolin- 
anum, Solidago sempervirens, and Distichlis spicata are scattered about irregu- 
larly. Spartina glabra is scattered plentifully in one place, 0 north by 1,050 
to 1,075 east. The southern border of the belt is exactly like the borders of 
patches in the preceding belt. At 110 south a large bed of Gerardia occurs, 
overlapping the border. On the east side the Spartina glabra belt projects 
into this. The north and west margins of the indentation are formed by the 
precipitous banks of a tide-creek, and the change of vegetation is correspond- 
ingly abrupt. The south margin isa sloping mud-flat. Here Distichlis spicata 
is established, and is vigorously invading. An isolated patch of Distichlis east 
of this may be a relic of an old mud-flat captured by the invading species and 
then cut off by a later advance of Spartina patens across the narrow isthmus. 
Will Spartina finally possess the patch and Distichhis withdraw? Atriplex 
patula hastata, Salicorma europea, and Spergularia marina occur in full 
development around this lobe of Spartina glabra. 'Total numbers of spermato- 
phytes, 10. 
In this belt Beggiatoa, both white and pink species, were noted in a pool at 40 
south, on the contour of 6 feet 6 inches, together with Anabena and mats of 
Rhizoclomum. 
About the zero-line the grasses grow shorter and other plants are more 
numerous among the Spartina patens. Distichlis spicata in particular appears 
in rapidly increasing numbers and Spartina patens disappears by equal steps, 
giving way to the Distichlis belt. 
6. THE DISTICHLIS BELT. 
For a short space Distichlis spicata is clearly dominant, but it is not sharply 
demarcated from the preceding belt. On the north, however, it stops with an 
abrupt but very irregular border at the edge of the tall Spartina glabra. The 
margin is fringed by runners of Distichlis advancing northward in the mud, and 
Spartina glabra has numerous outliers of one-half to one-fourth normal height 
in the borders of Distichlis. The narrow strip of soft brown mud (1 to 5 or 6 
feet wide) which is not closely occupied by either grass is copiously overgrown 
with Salicorma europea, together with numerous Sueda maritima, Atriplex 
patula hastata, and an occasional Atriplex arenaria. Scirpus nanus forms dense 
mats beneath everything else at several places on the border; at the east edge of 
the belt this species is quite exposed, forming the sole vegetation over 1 or 2 
square feet. Total number of Spermatophyta, 8. 
At 25 feet north Vaucheria thuretu forms dense tufts on the contour of 6 feet 
4 inches, and Rhizoclonium was found on a block of wood at the level of 6 feet 
6 inches at 25 north. 
