1924] Allen: Marine Diatoms and Dinoflagellates 247 
is important because it adds to the evidence that, under ordinary 
circumstances, temperature is not a directly determining factor in 
productivity of marine diatoms. 
In considering the evidence of productivity in this series of catches, 
it should be remembered that the southerly regions were traversed 
in late February (not usually a highly productive month), while the 
northerly regions were traversed in April (in some years the most 
productive month). For that reason, direct comparison of areas 
south of San Francisco with areas north of that point is rather 
unsatisfactory. So far as we really know, the southerly sections may 
also have been heavily productive in April. Still, it is not probable 
that the relative conditions of temperature were very different in 
the two months, since it is known that southerly sections get some of 
their coldest water in March and early April. 
At this time of year, the greatest change in any single environ¬ 
mental condition is supposed to be in the effect of the sun’s rays. 
There are excellent general and theoretic reasons for connecting 
vernal increase in productivity with solar influence, but, unfortun¬ 
ately, that is one factor concerning which marine researches are almost 
entirely lacking. 
Comparison of productivity of regions in this series with that 
of those in the 1920 series shows that the Destruction Island and San 
Francisco regions were highly productive in all three cases (McEwen 
in summer, Mortensen through fall, and the Pioneer in early spring). 
The Point St. George region was poorly productive in all cases while 
the Yakina Head region was most productive in Mortensen’s catches 
and very poor in MoEwen’s and those of the Pioneer. Thus we find 
additional evidence that some regions may be highly variable in pro¬ 
ductivity according to season or circumstance. On the other hand, 
it seems probable that some regions, e.g., Destruction Island, may 
always show relatively high productivity as compared with other 
regions. 
It is not possible at present to make a conclusive statement essen¬ 
tially different from that concerning the 1920 series (Allen, 1922). 
This is, however, an appropriate place to emphasize the fact that, with 
such vessels as the Pioneer, plankton collecting of very high value can 
be done, and that the spirit of cooperation shown by the officers and 
men of the U.S.S. Pioneer is exceedingly encouraging for more rapid 
and effective advances in oceanic research. The enthusiasm of the 
administrative officers of the U. S. Coast and Geodetic Survey in 
Washington is also encouraging and deserving of high commendation. 
