56 University of California Publications in Zoology [ Vou. 14 
where palms and other tropical plants flourish. The ripening of the 
former is retarded by the low prevailing summer temperatures, while 
the perennial vegetative growth of the latter is rendered possible by 
the absence of winter frosts. In the same latitudes, on the opposite 
side of the continent, tomatoes and Indian corn ripen as a matter 
of course, while palms and agaves cannot be grown out of doors. 
It is more than possible that the distribution of many marine 
organisms is similarly conditioned. It would be surprising if the 
occurrence of low temperatures during the period of reproduction 
did not limit the northward distribution of various species along the 
California coast, despite the relatively high annual mean and the 
absence of really cold waters during the winter. It is hoped that 
information bearing upon this point will be brought to light by those 
who are investigating the biological collections made in the course 
of the present survey. 
One possible instance of high economie importance deserves men- 
tion at this point. It is well known locally that the eastern oyster 
reproduces only sporadically in San Francisco Bay (see Townsend, 
1893), and it has been assumed that this is due, in part at least, to 
the comparatively low temperature of the water in summer. As we 
have shown above, however, and as was long ago pointed out by 
Townsend, there are shoal waters in the southern end of the bay 
where the summer temperature conditions are more nearly like those 
of similar points on the Atlantic Coast. Moreover the fact that in 
recent years even the spat which has been transplanted here from 
eastern waters has failed to mature satisfactorily, makes it seem 
probable that we must look to other causes besides temperature for 
the failure of the oyster to propagate in San Francisco Bay. We 
leave this problem, however, to those who are prepared to study it 
unremittingly in all its phases. 
VI. SALINITY 
The methods followed in obtaining and preserving the water 
samples for salinity determinations have already been deseribed 
(pp: 12; 13). 
The determinations were made in a laboratory on shore. The 
method employed was Mohr’s silver nitrate test, which indicated the 
percentage of chlorine in each sample. From this the salinity could 
