ITINERARY: FIFTH COMMISSION 303 



to the lowest that could be found, with a view to testing Professor Hardy's animal 

 exclusion hypothesis. The results obtained at these stations appear incidentally to 

 provide valuable proof that our methods are adequate for broad determinations of the 

 order of magnitude of the standing crop, of the type aimed at in this paper. 



At the New Year 1936-7 a line of stations was worked south-westwards across the 

 Scotia Sea, showing two fairly high values to the north. For the next six weeks the 

 ship was engaged on hydrographic survey work round the South Shetland Islands. 

 Plankton work was resumed in the middle of February with a line of stations worked 

 northwards across the Scotia Sea to the Falkland Islands. It was evident that the post- 

 maximal falling off was considerable. Early in March extremely varied quantities of 

 phytoplankton were observed round South Georgia, in keeping with our ideas of the 

 irregularity of the autumnal increase. 



The work of the fourth commission in the Antarctic zone was concluded by a cruise 

 eastwards to the meridian of Greenwich, mainly in the Intermediate Region, followed 

 by a line of close stations worked due northwards to the Antarctic convergence. The 

 chief result was a clear demonstration of an autumnal secondary increase in the Inter- 

 mediate Region in the latter half of March 1937. 



The phytoplankton observations obtained within the Antarctic zone during the fifth 

 commission of the R.R.S. 'Discovery 11' are shown in Figs. 8 and 9. The work falls 

 naturally into two parts: a circumpolar cruise, working on a zigzag course east about 

 from Cape Town, during the summer and autumn of 1937-8, and a long series of 

 repeated observations between o and 20° E, starting at mid-winter and continued 

 throughout the whaling season of 1938-9. 



Leaving Cape Town in November 1937, we first crossed the Antarctic convergence 

 on the 20th, and until 10 December when we were making our way northwards to 

 Fremantle, all the observations fell within the Northern and Intermediate Regions. At 

 first the quantities of phytoplankton recorded were small, though greater than the 

 minimal winter values. The main increase became apparent rather suddenly, the first 

 estimations exceeding 1000 units of plant pigments were recorded on 27 November 

 in the Northern Region and on 7 December in the Intermediate Region. Prior to this 

 the Intermediate Region was appreciably the poorer of the two. 



We sailed from Fremantle before the New Year and next crossed the convergence on 

 6 January 1938. Our zigzag course took us eastward mainly through the Intermediate 

 Region to the vicinity of the Balleney Islands before we worked north to New Zealand. 

 At the Balleney Islands we encountered an extraordinarily rich neritic phytoplankton, 

 and two stations near by showed that the main increase in the extreme north of the 

 Southern Region had begun by the third week in January. Throughout the main part 

 of this cruise it appeared that the main increase in the Intermediate Region was in 

 progress, but some low values were recorded, and it seemed that grazing might already 

 be causing local poverty. In the Northern Region the post-maximal decrease was 

 clearly apparent at the end of January. Grazing again seemed a possible explanation— 

 an extraordinary profusion of salps at this time has repeatedly been observed slightly 



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