THE PLANKTON -PHASE AND PLANKTON-IIATJE 7 



given by Raben for the Phosphorus -content (as ^fi^), at "14 mg. 

 per litre ; though according to Matthews the amount in the English 

 Channel (Plymouth, 1918) is much less, or -06 mg. per litre in 

 winter (maximum), and -01 mg. as the spring minimum, or as little 

 as one part in a hundred millions. There is nothing to show that 

 plant-organism can exhaust all the available N and P ions in the 

 solution ; and it may be noted that all such estimations have to be 

 made in the case of water already occupied by living plankton ; while 

 a considerable source of error must exist in the large amount of dead 

 and decaying or macerating debris of plasmatic organism which 

 apparently appears in analyses as " organic " nitrogen and "organic" 

 phosphorus (Matthews). Thus according to Raben the nitrogen 

 value rises in summer, as if from the greater death-rate at a higher 

 temperature ; and though Matthews accords a higher phosphorus 

 value in winter, it may be pointed out that his results for water taken 

 near the sewage outfall of a large town, presumably supplying 

 enormous quantities of microcosmic salt, give only *0G mg. per litre, 

 suggesting that excess phosphorus compounds are rapidly precipitated 

 as insoluble phosphates. From an interesting table of analyses for 

 various marine invertebrates (Delff, 1912), it may be taken as a 

 general estimate that the water-content of such organism varies from 

 70-90 7o» the nitrogen-content (N) from 5-10 7o> ^"^^ "the phosphorus- 

 content (P.Ps) as about -^th of the nitrogen value. This may be 

 probably taken as an approximate estimate for animal cytoplasm with 

 little waste ; and though plants with accumulated polysaccharide 

 debris would give a much lower rate for nitrogen, of possibly only a 

 third of this value (Brandt, 1898, p. 58) ; it may be also taken as 

 approximately correct for zoospores and mobile naked flagellates. 

 "With the sea containing nitrogen ions at about one in ten millions, 

 and plankton at the mean rate also of one in ten millions, it would 

 a])pear that the plankton of a litre would not cover more than ^-y^ 

 of the available nitrogen. In such case it is interesting to compare 

 the figures of Lohmann for total autotrophic plankton (including 

 Peridines) alread}'- given as suggesting an approximation to the 

 nitrogen limit, as also the later figures of Allen (1919) for a suggested 

 million of autotrophic organisms per litre (Diatoms, etc.), many of 

 which may be several times larger than the hypothecated 5 /a zoid ; 

 but the subject is again confused by the fact that we are still ignorant 

 of the actual cyptoplasmic value of a Diatom, as compared with the 

 " volume " of its vacuolated " cyst "-stage. Though the scarcity of 

 Nitrogen ions is not definitely established as a limiting factor for 

 pelagic life, the fact emerges that the actual quantities of living 

 material and the more essential ions of the medium are in a stiite of 

 somewhat comparable spatial tenuit}^ Although again clearly of no 

 veiT exact scientific value at present, such considerations are justified 

 as affording a general idea of the conditions under which living- 

 organism has been evolved in the aqueous phase of the sea ; and the 

 suggested "mean plankton -rate " may be useful in establishing some 

 general basis for the consideration of the economy of the phyto- 

 plankton and phytobenthon of the British coasts. 



