56 THE HANCOCK PACIFIC EXPEDITIONS VOL. 3 



mens to be in poor condition. Apparently, no great numbers were be- 

 ing devoured by copepods or other diatom feeders. The good condi- 

 tion of the diatom populations at so many stations also indicates that 

 the plants were physiologically ready to take advantage of favorable 

 external influences. Therefore, it is probable that very large abun- 

 dance might have been found a little later in numerous localities 

 where combinations of environmental conditions encouraged in- 

 crease of population. 



TEMPERATURE 



In general, it appears that the temperature tended to be progres- 

 sively lower toward the head of the Gulf, a large number of the mod- 

 erately large and large catches being taken at about 1S°C. Still, the 

 largest catch was made in a moderately high temperature of 19.4°C 

 just south of Tiburon Island, In 1921 (Allen, 1923) most of the large 

 catches were taken at temperatures near 20°C, but some were made 

 in water showing about 29°C. There can be no reasonable doubt 

 that temperatures have great influence on welfare and productivity 

 of plankton diatoms, but the relationships are too obscure to appear 

 as direct correlations in series of this kind. For one thing, it ought 

 to be more generally understood and recognized that a temperature 

 taken at the time of sampling a population of micro-organisms bears 

 no necessary relation to the immediate characteristics exhibited by 

 it. The temperature having most significant influence in causing the 

 visible condition of the sample must have appeared at some time 

 (possibly some place) preceding that of the sampling. The tempera- 

 ture taken at the time and place of sampling should be regarded only 

 as an aid to understanding the general status of the environment. It 

 should not be used for attempts to establish direct correlations. 



Summary 



1. There is ample indication that the Gulf of California provides 

 excellent opportunities for different kinds of phytoplankton investi- 

 gations. 



2. It appears probable that the more productive areas of the 

 Gulf lie between 25 °N and 30°N, and that conditions are more 

 favorable for phytoplankton production and maintenance toward 

 the north in that territory. 



