SECT. 21 ORGANIC REGULATION OF PHYTOPLANKTOM FERTILITY 193 



take place (Bernard, 1958, 1959). Daily collections in the Mediterranean show- 

 that Coccolithus doubles every five days (Bernard, 1958a) ; their growth in the 

 non-photic layers should then depend upon organic matter. Several Ghryso- 

 chromulina actively ingest particles (even graphite!) and cells up to 5 jj. (Parke 

 et al., 1955-1959) but none of the nanoplankton organisms has been grown in 

 bacteria-free culture and it is not known whether they can utilize dissolved 

 organic matter. 1 The fresh-water chrysomonad, Ochromonas malhamensis , 

 grows luxuriously in vitro on organic solutes ; it can also grow almost as well 

 phagotrophically or photosynthetically. Even supposing that the chrysomonads 

 living in non-euphotic zones of the sea are as versatile as Ochromonas nutri- 

 tionally, where do they find food to enable them to divide at least once in five 

 days? The content of organic solutes in sea-water is apparently quite low 

 (2-20 mg/1.) and bacteria are supposed to be very scarce in deep waters! 



G. Growth Factors 



The sampling of marine species in bacteria-free culture is indeed small but 

 it is clear that many marine photosynthetic algae need vitamins (Table VIII) ; 

 fresh-water algae behave similarly. A complete list of the vitamin requirements 

 of marine and fresh-water species is given by Provasoli (1958). Since then 

 J. C. and R. A. Lewin (1960) have studied the requirements of 26 species of 

 marine diatoms, Droop (1959) oiOxyrrhis marina, McLaughlin and Zahl (1959) 

 of two symbiotic dinoflagellates, and Fries (1959) of a red alga 2 (all included in 

 Table IX, with new results since ms. preparation). Table IX summarizes 

 the old and new data, including 23 species of Volvocales (Pringsheim and 

 Pringsheim, 1959). The tentative conclusions reached several years ago on only 

 two dozen species are still valid (Provasoli and Pintner, 1953). Briefly: (a) 

 photosynthetic algae, like autotrophic bacteria, have species that do not and 

 some that do need vitamins ( = auxotrophs) ; (b) only three vitamins are 

 required, alone or in combination; in order of incidence, vitamin B12, thiamine 

 and biotin (Table IX) ; (c) auxotrophy does not correlate with any particular 

 environment or with the lack or presence of heterotrophic abilities ; (d ) the 

 algae have an unexpectedly narrow and stereotyped need for only three vita- 

 mins even though the algae live in environments rich in all vitamins and many 

 accompanying micro-organisms (bacteria and fungi) have widely different 

 vitamin requirements. 



1 Organic carbon sources improve growth in light but cannot sustain growth of Hymeno- 

 monas sp., Pavlova gyrans, and Syracosphaera sp. in darkness. Coccolithus huxleyi has 

 very poor heterotrophic abilities (Pintner and Provasoli, in press). Some species oiChryso- 

 chrornulina are now bacteria-free. 



2 Since the writing of the MS the following species have been investigated : the diatom 

 Cyclotella nana requires B12 and Detonula confervacea has no vitamin requirement (Guillard 

 and Ryther, 1962); the Qhrysomonads Hymenomonas sp., Coccolithus huxleyi, Syraco- 

 sphaera sp., and Ochrosphaera neapolitana require only thiamine; Pavolva gyrans requires 

 B12 and thiamine (Pintner and Provasoli, in press) ; the blue-green Synechocystis sp. 

 requires only B12 (Van Baalen, 1961) ; the red seaweed Nemalion multifidum requires B12 

 and perhaps pyridoxamine (Fries, 1961). 



