PLANKTON OF THE GULF OF MAINK 465 



Elizabeth (station 10319) was chiefly C. serrala (Brandt, 1906, Taf. 39, figs. 4 and 6). 

 McMurrich (1917) records C. ehrenbemi and two species of Tintinopsis — T. cam- 

 panula and T. ventricosa — from St. Andrew.-;, while his unpublished plankton lists 

 note Cyttaroct/lift dtnticvlata and G. suhulata. 



According to Brandt (1910) the limits of C. denticulata in the North Sea area 

 are chiefly determined by temperature, its upper optimum being about 12°. In a 

 general way this is true also of the Gulf of Maine and of Nova Scotian waters, for 

 it is more numerous in the cold Nova Scotian current than in the higher temperatures 

 of the gulf, but the data are not sufficiently extensive to show whether its distribu- 

 tion within the gulf reflects the slight regional differences in temperature that prevail 

 there. 



OTHER UNICELLULAR ORGANISMS 



The reader must not assume that the foregoing notes exhaust the major groups 

 of unicellular organisms in the Gulf of Maine. On the contrary, such important 

 divisions as the coccolithophorids, the silicoflagellates, and the infurosia (apart from 

 the tintinnids) have not been mentioned at all, not because they do not occur but 

 because they have not been detected so far in our offshore hauls, or only on the 

 rarest occasions. Infusoria, in particular, may be expected to prove of considerable 

 ecologic importance when tow-net catches, preserved by methods suitable for these 

 minute and very delicate organisms, are intensively studied. Such, at least, is the 

 case in June in the Gulf of St. Lawrence, where the infusorian genera Mesodinium 

 and Laboea occur in abundance, as they do also in the waters off Halifax in May. 

 (Gran, 1919, p. 493.) The silicoflagellate genus Distephanus occurs at times in some 

 numbers at St. Andrews. (McMurrich, 1917, p. 4.) 



We have not detected Notiluca in any of the Gulf of Maine towings, though 

 its wide distribution in general and its seasonal abundance in the Irish Sea and 

 coastal regions of the North Sea region in particular, where it is one of the most 

 frequent sources of phosphorescence (Ostenfeld, 1910; Herdman, Scott, and Dakin, 

 1910), point to its presence in the gulf as probable. 



Globigerina is likewise to be expected in the gulf as an occasional immigrant 

 from the ocean waters of the open Atlantic, but is never likely to prove of any im- 

 portance in the Gulf of Maine plankton. 



NOTES ON THE BIOLOGY OF THE PHYTOPLANKTON 



Perhaps no phenomenon in the natural economy of the gulf so arrests attention 

 (certainly none is so spectacular) as the sudden appearance of enormous numbers 

 of diatoms in early spring, and their equally sudden disappearance from most of its 

 area after a brief flowering period. As precisely this same phenomenon takes 

 place in north European waters, where biologists have long occupied themselves 

 with the marine plankton, no wonder the possible factors, hydrographic and seasonal, 

 or the physiology of the diatoms themselves, which first permit and then estop 

 their almost inconceivably rapid multiplication and finally even prohibit their fur- 

 ther existence, have been the subject of much study and discussion. Nevertheless, 

 as Herdman (1920, p. 817) has recently declared, the factors governing this phenom- 

 enon still remain imperfectly understood. 



