48 THE HANCOCK PACIFIC EXPEDITIONS VOL. 3 



Whether in sea water or fresh water, those living attached to a solid 

 surface of any kind are called sedentary forms. Other kinds live 

 afloat in sea water or fresh water, and are called plankton forms. 

 The plankton kinds collected in this series were all obtained by dip- 

 ping six gallons of water from the surface of the Gulf and filtering it 

 through fine-meshed (200 meshes to an inch) bolting silk. The speci- 

 mens caught on the silk were preserved in ordinary formaldehyde. 



These 1936 catches were especially important because it was the 

 first time that any had been made in the Gulf in late winter or early 

 spring, the season at which microscopic plants as well as other plants 

 are likely to show increased growth and abundance in nature. In the 

 ocean off southern California there is a wide range of differences in 

 times of greatest abundance of plankton diatoms in different years, 

 but there are more years in which largest abundance occurs in spring 

 than there are showing largest abundance at some other season. 

 Therefore, it is reasonable to suppose that the Gulf of California 

 tends to yield in large abundance at that season. 



Taking Cape San Lucas as the outer limit, eighty catches were 

 made in the Gulf, thirty-seven while northbound, forty-three south- 

 bound. The round trip occupied a little more than a month, involving 

 important time differences in the sampling of different sections and 

 localities. For convenience in discussion, three sections may be desig- 

 nated, i.e., southern, south of 25 °N; middle, from 25 °N to 27°N; and 

 northern, north of 27°. In respect to time, each of these three sections 

 differs from the others, not only as to the dates of sampling, but also 

 in the total time elapsed between the taking of the first and last 

 samples in the section. All of the catches in the northern section 

 were taken within two weeks of each other, while those in the south- 

 ern section were taken in two periods three weeks apart. Further- 

 more, the two weeks of operation in the northern section were mid- 

 way between the periods of operation in the southern section, and 

 there is no means of knowing how conditions in the one compared 

 with those in the other at that time. This point of time difference is 

 stressed, not because of any unusual deficiency in the series, but 

 because it cannot be ignored when catches are repeated at certain 

 stations at intervals no longer than these. 



If collections had been made only on a continuous trip in one direc- 

 tion, this particular kind of comparison of the localities would not be 

 suggested by the records, at least not strongly. If collections in all 



