6 THE PLANKTON-PHASE AND PLANKTON-BATE 



apparently solely of polysaccharide excreta ; chitin is rare, and may 

 be probably taken as evidence of heterotrophic nutrition (Peridines). 

 All primary life in the sea must be considered as autotrophic^ the 

 animal life dependent on it need not be taken into consideration at 

 all. So far as the plant is concerned this *' Mean Plankton-rate " 

 may be taken as a rough basis of comparison, and a convenient unit 

 to remember ; and thus without necessarily impl^dng that such a rate 

 bears reference to the total autotrophic plankton of sea-water, it may 

 still be used as a fair average unit of comparison in the case of each 

 organism separately' ; since in the case of either the benthic fish or 

 the benthic sea-weed, the plankton return is localized and subject to 

 infinite dilution in the moving medium ; while in the case of free 

 pelagic plankton -forms the complex relations of physical conditions 

 imply that only a few types are dominant at any particular pei'iod. 

 It is interesting to compare Lohmann's maximum rate for Kiel Bay, 

 given by the Diatom Skeletonema costatum (at 5 fathoms in August), 

 with an average of 9 millions per litre, or approximately 10 per cubic 

 millimetre ; assuming a volume of 150 c. /x (Lohmann, p. 2-11), this 

 implies a total plankton-rate practically 15 times that of the mean. 

 Lohmann {loc. cit., p. 351) also gives the maximum plankton -yield 

 for all '* plants " (autotrophic, and including all pigmented flagellates) 

 in August, as equivalent to a volume of 105 ••! c.mm. per 100 litres ; 

 i. e. 1-05-1 c.mm. per litre, or one part in a million, as an average rate 

 10 times the above mean. For Ceratium tripos, with an estimated 

 volume of 100,000 c. //, (Lohmann), the plankton-rate would work 

 out as 1000 per litre, — the maximum given for all Peridines at 

 Plymouth (June ; Lebour, p. 153) ; while Lohmann (p. 276) for 

 Kiel, gives th« plankton-rate of C. tripos (var. lalticiini) as 4 per 

 litre in winter, rising to a maximum average of 4590 per litre in 

 August, and the maximum range as 13,000 per litre (November, at 

 5 fathoms), thus agreeing with a value 13 times the suggested mean. 

 An estimate for heterotrophic Bacteria in London sewage of only 

 5 millions per c.c. = 5000 millions per litre, or 5000 per c.mm. ; and 

 assuming a volume of 5 c. /x, this works out at 100 times the mean 

 plankton-rate, and the estimate may be doubled. The plankton-rate 

 of Yeast ma}' be on a similar footing, as also that of hemi-holozoic 

 Euglena in manure- water ; these being like Bacteria special cases of 

 ht?tero trophic nutrition dependent on elaborated organic food-supply 

 other than ions of simple salts. For example, a laboratory' culture of 

 the apparently holozoic Cryptomonad Chilomonas, living as " Sapro- 

 plankton " in pool- water, gave an estimated content of 4000 per 

 " drop," or about 80 millions per litre. Taking this large flagellate 

 as of approximate volume of 1000 c. />t, the plankton-rate would work 

 out as 2400 times that of the suggested mean rate ; such a culture 

 again remained healthy and intensely active for several months 

 without any indication of toxic effects, while surface-aggregation 

 might represent a rate of 40,000 per drop. 



Observations by Raben (1910, p. 310) give the total Nitrogen- 

 content of the sea (Mediterranean and North Sea) as sometliing 

 between '1 and 2 mg. per litre (rarely exceeding -2), or -0001 g. 

 per litre = 1-2 parts in ten millions also ; a very similar result was 



