240 RiGG: SALINITY AND THE DISTRIBUTION OF NEREOCYSTIS 
exactly this temperature, while the samples from the kelp bed 
and the open Strait varied from 12.5° C. to 13.5° C. There was 
found to be no difference in the hydrometer readings taken in the 
open Strait and those taken at any of the points where kelp grew 
inthe bay. The reading taken in the mouth of the river was zero. 
The reading taken about 500 feet straight out from the mouth of 
the river showed about one third as great a salinity as the water 
of the Strait and of the bay. 
The facts are, then, that a strong tidal current sweeps freely 
through this kelp bed, and the water at all points in it shows the 
normal salinity of the water of the Strait. So far as this bed is 
concerned kelp does not grow in water that has less than the normal 
salinity. It does not seem quite possible, however, to say posi- 
tively that the lack of normal salinity is the only inhibiting factor 
preventing the growth of kelp near the mouth of the river, al- 
though it seems to the writer that such is probably the case. 
Outside of the question of the salinity of the water, there are at 
least three factors that limit the distribution of Nereocystis in the 
Puget Sound region. These are rocks for anchorage, a strong tidal 
current, and proper depth of the water. The strong tidal current 
is present at the mouth of the river, as it is in the other portions 
of the bay, and the water is of proper depth for kelp, a little 
distance off shore, as it is in the other portions of the bay, where 
kelp does thrive abundantly. It may be possible that the silt 
brought down by the river has so covered the rocks near the mouth 
of the river as to render the attachment of kelp impossible. 
Two sets of samples were collected—one set from the extreme 
western end of the bed (over three miles from the mouth of the 
river) and one set from the extreme eastern end (the portion of the 
bed nearest the mouth of the river). The analysis of these 
samples is shown in the following table. 
The above figures should not be construed as indicating posi- 
tively any characteristic difference in the potash content of the 
kelp from the two ends of the bed. It will be noted that sample 
number 3 has a much higher potash content than any other sample 
reported in the table. Neglecting this one, the samples from the 
west end of the bed average about one per cent higher in potash 
than the samples from the east end. This, however, should be a 
ah 
