THE PLAXKTON-PHASE AKD PLANKTON-RATE 3 



comprehensive view of the relation of plant and animal forms, as also 

 their seasonal periodicity. For example, maximum monthly averages 

 give: — Skeletonema costafum in Jmie at 2,460,000 per litre ; all 

 other Diatoms 20,000 per litre ; Grreen Flagellates (July) 146,800 

 per litre ; Peridiniacea? (July) 382,000 per litre ; or taking all pre- 

 sumed autotrophic organism, over two millions per litre in May, over 

 two and a half millions in June, and over half a million in July. 

 Taking a litre as a million c.mm., a million per litre means 50 in a 

 ** drop." Lebour, for Plymouth (1917), gives total Diatoms in April 

 as 40,000 per litre, or 2 per drop, and the June crop of Peridiniacege 

 as 1000 per litre ; though in this case the smaller and more naked 

 organisms are probably wholly lost. The consideration of Bacteria 

 may be omitted, as these must be considered heterotrophic ; but 

 immense numbers of algal zoospores, or units even of the 100 /a 

 standard of Fucus oospheres, are again apparently irrecoverable. 

 Special interest attaches to recent observations by cultural methods 

 (Allen, 1919), since these ignore the question of heterotrophic 

 Bacteria, all purely holozoic forms, as also holozoic Peridiniacese ; 

 these last rapidly die on removal from open water, and the organisms 

 which will grow are practically restricted to holophytic Diatoms and 

 a few Brown Flagellates, etc. The number of such recognizably 

 holophytic plankton-forms is given as at least 464,000 j^er litre, or 

 464 per c.c, about 23 per drop, with the suggested possibility of 

 there being really a million per litre. In this case, control observa- 

 tions by centrifuge-methods gave a total estimate of only 14,450 per 

 litre and thus illustrated their imperfection (M. B. A., Plymouth, 

 Sept. 1918). In view of such data, it may be pointed out that we 

 are still far from knowing the limit of living organism in the sea, 

 or what may be the material on which minute flagellates and Peri- 

 dines feed. 



The recognition of the primary autotrophic nature of phyto- 

 plankton, again presents a greater botanical interest, in that, putting 

 all holozoic races on one side as of secondary importance, the problem 

 of Plankton enters on another stage as representing an older condition 

 of life in the sea conceived as a " Plankton-Epoch," before the evolu- 

 tion of any benthic life had been rendered possible by the rise of the 

 sea-bottom to within a distance of 100-50 fathoms from the surface. 

 This may be regarded as the expression of the first stage of biological 

 life on this world, as existing, and in fact evolved, in the surface- 

 water of the primal universal ocean, directly from the sea-water itself. 

 The conception of Plankton thus acquires a Fhyletic significance ; 

 and this Plankton-Epoch, including a period of indefinite millions of 

 years, in which living organism acquired the morphological and 

 physiological organization of what is now known as the " cell " from 

 nothing at all but ionized sea-water, — once universal and the 

 highest expression of living organism — is now represented in the sea 

 by residual races, more or less isolated and specialized, or vestigial, 

 which may be said to survive in the *' Plankton-Phase " ; though 

 higher forms of life have passed on to successively higher stages with 

 the introduction of the physical factors of sea-bottom and dry land. 

 It is, in fact, from such races that we liave to build up our conception 



