THE PLANKTOX-PHASE AND PLANKTOJf-RATE 5 



aim and mark of higher organization, i, e. organism. The wastage 

 of a Saccorhiza in a plankton-phase, to the extent of 300,000 million 

 or more of 5 /x zoids, is the expression of the cost of the race to the 

 individual. The increasing intensity of the incidence of wastage in 

 the case of emergent Land Flora is simply expressed by the fact that 

 in the common Fern, Aspidium FilLv-mas of to-day, the spore 

 output of a single plant may be estimated at 500-1000 million of 

 air-borne spores of 50 /x diam., or each 1000 times the volume of the 

 Phseophycean zoid ; while the spore-output of a single staminate 

 strobilus of Araucaria hrasiliensis, of 1000 stamens, has been 

 estimated at ten million spores of 50 ix diam. (Burlinghame, 1913). 

 Such air-borne spores are, it is true, no longer plankton, but they are 

 the lineal descendants of the immobile " tetraspores " of benthic sea- 

 weeds, in which flagellation has been suppressed in correlation with 

 increasing bulk. 



A little consideration, again, suggests that such a plankton-rate, 

 of a million per litre, is one per cubic millimetre, and a volume of 

 100 c. /x in 1,000,000,000 c. /x is one in ten million (taking volumes 

 as approximately equivalent as densities). The generalization that a 

 fair plankton -rate may be approximately equal to the ionization of 

 the H.^0 onl}^ is sufficiently striking, although the two phenomena 

 have clearly no causal relation ; since the mass of the water affords a 

 practically infinite source for the production of further H", OH' ions, 

 if an}^ be removed ; while the limiting factor for the amount of life 

 in tlie sea has been very generally accepted as due to the scarcity of 

 ions of Niti'ogen and Phosphorus. Hence in coastal waters, or in the 

 enclosed shallow Baltic, the plankton-rate rises considerably as com- 

 pared with the English Channel, Mediterranean, or open Atlantic. 

 The Sargasso Sea affords an interesting case : — the Gulf-We^d 

 vegetating as a sparse crop in the surface-water possibly takes the 

 greater part of the available N and P ions, giving nothing back 

 directly, as it is wholly sterile, and dead plants sink in two miles of 

 water ; hence there is little scope for other autotrophic life, and beyond 

 the hosts of small animals feeding on the weed and on each other, the 

 Sargasso Sea is conspicuous!}^ sterile. [Total Plankton-rate 5000 per 

 litre, plant-cells, all sorts, including Peridines (Murray and Hjoi-t,, 

 p. 365) net-results only, admittedly imperfect and much too low; 

 while there is no strict justification for regarding the Sarr/assinn as 

 more intensely proteid-metabolizing than the autotrophic plankton.] 



The fundamental factors which determine the amount of plankton- 

 life the sea can carry remains still extremely obscure ; as previously 

 indicated, the supply of N and P ions has been put forward (Brandt's 

 Hypothesis, 1902) as constituting a limiting factor for autotrophic 

 organism ; for holozoic organism food and the amount of available 

 oxygen are obviously significant, and for Bacteria also the amount of 

 special " food-material " to be metabolized. Zoologists have shown a 

 tendency to assume that the amount of holozoic organism must be 

 limited by the toxic effect of nitrogenous waste and excreta (Johnstone, 

 p. 28(3); but the botanist is not sensitive on these points; there is 

 no evidence of nitrogenous waste in the plant ; the membranes are 



