150 SIR W. A. HERDMAN : RESULTS OF CONTINUOUS 
There is some evidence to show that the autumnal increase in plankton 
may be more closely dependent upon the weather of the moment than is the 
case with the spring maximum, and that, in fact, there is no very marked 
autumnal rise, unless the weather conditions are favourable. For example, 
in September 1907 a sudden increase in the phytoplankton coincided with 
the highest sea-temperatures of the year, and, at the same time, a week of 
fine calm weather with light easterly winds. Then, again, the summer of 
1911 was exceptionally dry, warm, and sunny, while that of 1910 had been 
cold, gloomy, and stormy. August 1911 had 194 hours of sunshine recorded 
at Port Erin as against 80 hours in August 1910, and about 107 as the 
average for August of the previous four years; and any effect of this 
enormous increase in the August sunshine may naturally be looked for in the 
autumn and winter plankton, and possibly even in that of the following 
spring. We find, then, that the secondary diatom maximum in the late 
autumn of 1911 was unusually large. The numbers for the diatom monthly 
averages, per haul, in the two years are as follows :— 
August (1910)... 85 (1911)... 1,998 
September |, ... 676,82: » 928,501 
October yee 008,601 „o. 4,742,791 . 
November e 0. 100,262 » 506,729 
Thus, in 1911, the year of the remarkable August sunshine, the October 
phytoplankton was about nine times as great as in the previous vear with 
the gloomy summer. Moreover, in the following spring (1912) diatoms 
made their appearance unusually early and in vast quantity. Nearly two 
millions per haul were reached on March 11th, and nearly 25 millions on 
March 21st, and these high numbers were kept up till the middle of June, 
the actual maximal haul being over 200 millions on May 30th ; whereas in 
the spring of 1911 the millions were not reached till May 10th, and the 
numbers had dropped again by June 12th, the maximal haul being under 
70 millions on May 16th. The Dinoflagellate maximum was in 1912 a 
month earlier than in 1911, and had on May 9th a haul of over 8 million 
Peridinium, the greatest number recorded in these series of investigations. 
Thus, the weather of the previous summer and autumn may have an effect 
upon the phytoplankton of the next spring and summer. 
The contrast between a typieal phytoplankton (diatoms and dinoflagellates) 
in late spring and a typical zooplankton in summer is shown well in the 
following record of the united monthly averages in the two cases :— 
1911. Phytoplankton. Zooplankton. 
May + June ... ... 28,046,330 ... a.. 98,333 
July + Aug. ... .. 30,684 ... ... 238,215 
These are not the largest hauls, but only monthly averages, but the 
differences are quite sufficient to show the change in the nature of the pre- 
dominant plankton in passing from the one period to the other. 
