6 THE RELATION OF PLANTS TO TIDE-LEVELS 
The purpose of these studies has been to determine and record the distribution 
of the plants occurring in this harbor in relation to external conditions. The 
external factors considered are: topography, substratum (including subsoil), 
and salinity of soil-water; the time of submergence and exposure due to tides ; 
water-currents and the effect of immersion in fresh water during low tide. An 
attempt has been made to determine, as far as is possible from direct observation, 
which of the various external factors are the effective ones in determining the 
distribution of each plant or plant society. 
It is believed that such a record of the present distribution of the plants of this 
harbor, in relation to external conditions, will be of value in several ways. In 
the first place, the vegetation in question will serve as a type for many of the 
harbors on the north side of Long Island and on other parts of our coast. 
Secondly, the relative importance of the various factors affecting the distribution 
of marine plants in general may be perceived in part from a consideration of the 
conditions here described. Thirdly, it is also true that a comparison of the 
conditions and the plant distribution existing in this area two or three decades 
hence with those here recorded should indicate to what changes in conditions 
any changes in the distribution may be due. Such a comparison will certainly 
aid in giving a clearer conception of the causes of plant succession among littoral 
associations. Fourthly, in this general study of the factors affecting the 
distribution of these plants, the particular problems likely to yield valuable 
returns for experimental study have become more clearly defined. It is well 
understood, of course, that most of the problems of distribution here dealt with 
can not be adequately solved till the physical conditions of the environment are 
accurately measured. 
