C'AXADIAX FISUKRIES I.X I'KDn li)\, I'Jt'rlo 491 



the gulf of St. Lawrence, according- to the same method as we have followed in Europe. 

 The method is, it must be admitted, not without certain limitations, and these become 

 more than usually apparent when dealing with a water whose phytoplankton is less 

 known, or where, at any rate, the annual periodicity of the species, a point with which 

 we are here especially concerned, is very little known indeed. The comparatively small 

 samples offer no occasion for critical consideration of the species from a systematic 

 point of view, or for description of the rarer forms. All species of common occurrence 

 are, however, well known from the North-European waters, so that this is only of 

 minor importance. A more serious difficulty is the fact that an investigation such 

 as the present can naturally give widely different results at different seasons of the 

 year, and it will consequently be impossible to determine at what season the samples 

 should preferably be collected, when seeking to obtain, from a limited quantity of 

 material, a view of the characteristic features in the production of the water con- 

 cerned. 



The present material was collected at two different seasons, in early summer 

 (May 29 to June 15) and, later on, in August. The former period would, on first 

 consideration, appear very favourable, provided that the conditions prevailing were 

 anything like those of Northern Europe; we should at this time expect to encounter 

 the transition between the rich spring plankton and the incipient development of the 

 summer plankton ; in August, on the other hand, the summer plankton should be near- 

 ing its culmination, though this would probably not be actually reached until Sep- 

 tember. 



The results show us a plankton essentially consisting of the same species as are 

 also found on the other side of the Atlantic, but which is both qualitatively and 

 quantitatively poorer than that of the European waters. We must doubtless reckon 

 with the possibility that the greatest maxima are found at other seasons of the year 

 than those covered by the present investigations; this is, indeed, more than likely 

 to be the case. In the North-European waters, the diatoms have their maximum 

 in March- April, when the surface temperature is at the annual minimum; this 

 mass development of diatoms is here composed chiefly of northern, and to some 

 extent of Arctic species with low temperature optimum, and the Arctic character 

 becomes more and more pronounced farther to the north. Such a maximum was 

 encountered in the gulf of St. Lawrence on the 11th of May, when no plankton samples 

 were taken for quantitative investigation, but only qualitative samples, taken in the 

 ordinary nets. These samples were very rich, and consisted of markedly Arctic 

 species, a community such as we find in May-June off the coasts of Greenland or in 

 the Barents sea, or, to a less pronounced degree, off the northwest coast of Norway in 

 April. It also exhibits great resemblances to the plankton described by P. T. Cleve 

 from the water about Disco island in May, 1894.1 



1 P. T. Cleve, Diatoms from Baffins Bay and Davis Strait, collected by M. E. Nilsson, 1896, 

 Bihang till K. Svenska Vet. Akad. Handlinger Bd. 22 Afd. Ill, No. 4. 



