494 DEPARTMENT OF THE NATAL SERVICE 



sea. The vertical distribution is peculiar; at station 6 we find Lepiocylindrus danicus 

 almost evenly distributed from surface to bottom, though with a certain increase in 

 numbers toward the lower levels. We may be justified in concluding that this even 

 distribution is a result of vertical movements, either of the water masses or of the 

 diatoms themselves, which, after a rich development at the surface, have then sunk 

 down to deeper layers. At station 8, this development is somewhat further advanced; 

 the rich diatom plankton has almost disappeared from the warmer and somewhat less 

 saline surface layer, and is first met with at 30 m. and thence down to the bottom. 



Leptocylmdrus danicus represents, on the coasts of Northern Europe, the last 

 phase in the development of the spring diatom plankton, and the same appears to be 

 the case in the waters here investigated, where the development already seems to be 

 nearing its conclusion in the last week of May. Here, however, we do not find, as we 

 do in Europe, any rich plankton of Cilioflagellates ready to replace the diatoms; these 

 organisms have their optimum at higher temperatures. The most northerly of these 

 species, Ceratium arcticum, is found, it is true, especially at station 10, but in small 

 quantities compared with the numbers of Ceratium found in the coastal waters of 

 Europe. Only at station 14, where the surface layer has attained a temperature of 

 8-l°C, do we find any considerable quantity, especially of Ceratium longipes. 



Cruise of the " Princess '" August 4 to 5, 1915 (Table 3). 



On investigating the gulf of St. Lawrence in the first days of August we might 

 expect to find the results of the summer influence upon the plankton development 

 typically represented. The present investigation, however, reveals a remarkably poor 

 plankton. From what we know of the European waters, we should hardly expect, at 

 this season, to find any considerable quantity of diatoms; and they are also but very 

 sparsely represented in our samples. August should, however, be the right time for 

 Cilioflagellates, especially Ceratium and Dinophysis species. Of these, we find 

 Ceratium, fusus and longipes quite abundant at the two first stations (29 and 30) ; 

 otherwise, however, they are somewhat scarce. The genus Dinophysis is represented 

 by Dinophysis norvegica, the occurrance of which corresponds to that of the Ceratium 

 species. Ceratium tripos, which, with C. fusus, is distinctly euryhaline on the coasts 

 of Europe, is here altogether lacking, as also C. fxirca. Of infusoria, we find the 

 interesting Lahoea strohila abundant at station 29; otherwise all species occur but 

 sparsely. As, however, these samples were preserved with formalin, which is far less 

 calculated to preserve the more delicate forms than Flemming's liquid, the result may 

 be somewhat misleading in the case of the infusoria; with Diatoms and Cilioflagel- 

 lates, on the other hand, this method also is thoroughly efficacious. 



As a general result, then, we may say that the phytoplankton of the area investi- 

 gated appears to be in quantitative respects considerably poorer than at the correspond- 

 ing season in the North sea; on the coasts of Europe, we find a secondary maximum 

 in September-October, when the surface layers are driven in towards the shores; and 

 we might expect to find something similar also on the other side of the Atlantic. 

 The present investigations seem to show that the general character of the plankton 

 has an annual periodicity similar to that noted on the coasts of Europe, though com- 

 mencing somewhat later, with the psychrophile species more predominant, while a 

 number of the thermophile forms of Northern Europe are lacking, or occur but 

 sparsely. The relative poverty in an area such as the gulf of St. Lawrence, which 

 with its rich supply of fresh water, should ofi^er, for the diatoms especially, good con- 

 ditions of nouT-ishment, is somewhat surprising; possibly it may be connected with the 

 rapid alterations in hydrographical conditions. On the coast of Norway, the develop- 

 ment of the diatoms commences in February, and not until May is the 

 rise of temperature in the surface layers so perceptible that the develop- 



