82, THE RELATION OF PLANTS TO TIDE-LEVELS 
threes, over a beach covered chiefly, though often sparsely, by either Sueda or 
Salicornia europea. There is one group of a dozen of these perennial Salicor- 
nias between 790 and 820 east, of which most are 6 or 8 dm. across the individual 
plant (plates 11 and XIII). 
The distribution of the two species of Salicornia: From what has been said 
above of the distribution of these two Salicornias, it is evident that the concur- 
rence, in any area, of all the conditions allowing the establishment of a dense 
stand of either is rather rare on the shores of this harbor. Even the thinner 
stands occur in but a few and relatively small areas, except on the Spit. We are 
unable to do more than suggest the possible factors influencing the horizontal 
distribution along the shore. We have been unable to discover any very probable 
determinant of the vertical distribution of these two plants. It seems evident 
that the horizonal extent of the patches of the annual S. europea, along the 
beach, is determined by its perennial competitors, especially by Spartina patens 
and Distichlis. The seedlings of this Salicornia can start only on unoccupied 
soil, which means either soil that has been bared of its competitors or soil that 
can not be successfully occupied by them, even with their advantageous habit 
of spreading to adjoining territory by means of their rhizomes. It will be 
interesting to note in this connection that in early April 1911, when the beach 
was still bare of vegetation after the winter, many seedlings of Salicornia, 
probably S. ewropea, were found on the Spit far beyond the areas that are oc- 
cupied by mature plants in summer. Many of them, for example, were found on 
the mud between the dead stumps of the Spartina glabra, down as far even as the 
5-foot level. Others had started higher up, where they would be sure, later on, 
to be shaded out by the rapidly growing shoots of Spartina patens. 
Shreve, and also Chrysler (Plant Life of Maryland, p. 131 and p. 178), have 
suggested that Salicornia europea grows on areas where the soil-water is subject 
to concentration by evaporation, and that the high salinity so attained is really 
the factor that determines the occurrence of Salicornia on these areas. This 
assumption would not adequately explain the distribution of this species at 
Cold Spring Harbor, for here, as we have seen, it grows luxuriantly on beaches 
the soil of which is flushed out by a submergence of from 3 to 3.5 hours each 
tide. Moreover, S. ewrope@a grows on the point between two streams, at 440 
south by 770 east, just above the 6-foot level, where it must be overflowed by 
fresh water for at least 3 or 4 hours daily. As the tide rises the fresh water of 
the two streams is backed up north of the causeway, and it is not until the tide 
has risen to at least a foot above the substratum that the layer of fresh water 
next the substratum is replaced by salt water. Salinity tests made at this point 
show specific gravities of soil water of from 1.015 to 1.017. It is to be remarked, 
however, that Salicornia has never been found growing where fresh water is 
constantly present in the soil or flowing over it at low tide. 
The Salicornias, at least S. europea, grow on either muddy, sandy, or gravelly 
soil, though the denser stands of both species are found on the gravel. All soils 
bearing either Salicornia have at least moderately good drainage, for example, _ 
when growing near tide-pools it is always on the more elevated parts of their 
margins, above the constant water-level. Salicornia is found in well-lighted 
areas, in the open sunlight, except for the little shade given it in some places by 
the neighboring Spartina glabra. Neither Salicornia has been seen on the west 
side, where the conditions are apparently otherwise favorable, but where, as we 
have seen, these levels of the beach are deeply shaded for half the day. 
