1923] Allen: Statistical Studies of Marine Diatoms 447 



Details of the hydro-graphic data do not have demonstrable con- 

 nection with changes in the diatom population. Specific gravity was 

 extremely low once and temperature extremely low four times (as 

 compared with the mean) on the first trip. If these extremes be 

 dropped from consideration it may be said that both temperature and 

 specific gravity were slightly lower on the second trip than on the 

 first. There was also much more clear weather, especially at the time 

 of lower temperature, on the second trip. The larger catches of the 

 second trip were all made at temperatures slightly above or very near 

 the mean. 



MATERIAL COLLECTED 



As shown by table 1 catches on the first trip were very light, only 

 one (made about twenty-three miles west of San Diego) containing 

 more than 1000 to the liter. On the second trip all catches in the 

 first section were over 2000 to the liter, four out of five in the second 

 section were over 2000, and two out of four in the third section were 

 over 3000 to the liter. While section four (directly south of Sati 

 Clemente Island) and section five (nearer to Cortes Bank) yielded 

 very small catches, the catches were nearly all larger than catches 

 from these sections on the first trip. 



Such conditions obviously indicate not only an abrupt change 

 from the non-productive winter season, but also that the causes of 

 change were operative over an area nearly ninety miles in width, 

 extending from the coast line two-thirds of the distance across the 

 continental shelf. Non-microscopic, casiial inspection of material 

 collected at the La Jolla pier shows close agreement with this indi- 

 cation in that production increases with the beginning of February 

 and reaches its highest for that period about. February 12. 



Diatoms. — On the first trip twenty-six species of diatoms were 

 caught, on the second trip, thirty-five. These included practically all 

 of the species which attain numerical prominence at any season. It 

 therefore seems probable that prominence of particular species at 

 certain seasons is due to especially favorable conditions rather than 

 to wholesale migration into the local field. I do not think, however, 

 that this view invalidates the supposition that drift currents may 

 sometimes sweep a large population into any given area. Either or 

 both may account for increased production, according to circum- 

 stances. 



