104 THE RELATION OF PLANTS TO TIDE-LEVELS 
penetrate into the soil. Such observations as we have made seem to show that in 
summer the salinity of the soil water above the 9-foot level, at least on the south 
side of the Spit, is not very high. These would be in accord, therefore, with the 
results obtained by Kearney (1904) on the coasts of Virginia, Massachusetts, 
and California. 
Relatively few of the upland plants are able to withstand the conditions 
encountered near the mean high-water level, 1. e., below the 9-foot contour. 
Those whose lower limit of distribution is below 9 feet are the following: 
Agropyron, 8.25 feet; Chenopodium, 8.5 feet; Galium, 8.5 feet; Panicum, 8.25 
feet, and Poa pratensis, 8.25 feet. Once we get above the 9-foot level, and thus 
clear of the influence of summer storms, the conditions become endurable for 
a much larger number of species. In fact, we find at the 9-foot level, on the 
shore, or in depressions in the top of the Spit, the only habitats on the Spit for 
certain species which apparently can not withstand either the greater salinity 
of the soil-water lower down the beach or the greater dryness higher up. This 
seems true, ¢. g., of Allium, Anaphalis, Gleditsia, and Oxalis. Other species, 
on the contrary, can endure any conditions found on the Spit except the more 
saline soil-water found below 9 feet. That is, they range upward from this 
level to the very top of the Spit, at 11 feet or higher. Such species are Ambrosia, 
Asparagus, Eragrostis, Mollugo, Polygonum, Psedera, Rhus toxicodendron, 
and Setaria. Another series of species have been found only at these higher 
levels. Thus, e. g., our records show the following plants to have their lower 
limit between 10 and 11 feet: Cyperus, Lactuca, Poa compressa, Polygonella, 
and Portulaca. Finally, another series still of the plants of this belt, which 
includes most of the woody species, have not been found growing below the 11- 
foot level. The chief of these are, Atlanthus, Nepeta, Oenothera, Quercus, Rhus 
glabra, Robima, Saliz, and Taraxacum. 
The further details of distribution of the plants of these levels on the Spit 
are shown in plate xIv, in which the individual plants of a selected transverse 
strip of the Spit are indicated by a symbol for each individual, except in the 
case of a very numerous dominant species. The significance of this chart, and 
of plate Iv, giving the zonation of vegetation on another selected part of the 
Spit, will be made entirely clear by the full explanation accompanying each 
of them. 
2. THE SUPRA-LITTORAL BEACH, OR STORM BEACH, OF THE EAST AND WEST SIDES OF THE 
HARBOR (FROM 8 TO 10 FEET). 
On the east side of the harbor there is, as noted above, no really natural shore 
north of the mill at 500 north (plate 1). There is, however, a border of rather 
gravelly soil between the 7.5 and 9 foot levels, extending from about 800 north to 
1,150 north and including the eastern half of the stone pier. The wall of the 
wharves here varies from 7.5 to 8.5 feet in height and is often of loosely laid 
stones, which allows the water to wash away the soil behind the wall, often down | 
to considerably below the top of the latter. This strip of shore has somewhat the 
character of the same levels south of the mill, except that it has fewer fresh- 
water streamlets. The vegetation of this soil includes half a dozen species 
characteristic of the upper littoral beach, already referred to (pp. 74-90, etc.). 
There are also 3 species here that are found on the storm beach of the Spit. 
