504 CYCLES OF ORGANIC AND INORGANIC SUBSTANCES 



Almost before they were made, however, such experiments were 

 liable to several kinds of criticism (e.g., Tailing, 1957). Even 

 though a relationship might be established in vitro, do the same 

 conditions ever, or reasonably frequently, hold in nature? Even 

 though a substance is demonstrably produced, will it not rapidly 

 be modified in nature? Even though organisms may have de- 

 monstrable metabolic requirements, such as for Bio, are these 

 metabolites ever scarce enough in nature to be significantly 

 limiting? Alternatively, does the hypothesis postulate so many 

 variables that we can never hope to disentangle them? Again, 

 criticisms have been raised that some of the effects demonstrated 

 or postulated are not typical of the normal, active life of the 

 organism mediating them but only of its decay. This is perhaps 

 the simplest to refute, since all organisms are subject to decay. 

 Ecologically speaking the stage at which the metabolites are pro- 

 duced is less relevant. What is significant is that following their 

 decay other and specific organisms "succeed," sometimes literally 

 amidst the fruits of that decay. 



The other criticisms are more serious, if only because they are 

 more difficult to answer by experiment and observation. Informa- 

 tion we ha\'e to date about B12 in nature pro\'ides a good example. 

 Among others, Cowey (1956) demonstrated (with samples collected 

 by Dr. Johnston from our research vessels) that an annual cycle 

 of B12 content might be presumed, and Droop (1957), to whom 

 we owe so much in this particular field, was led to suggest that so 

 slight were the phytoplankton requirements in terms of B12 that, 

 even at Cowey's lowest values, there might always be ample 

 supplies for the greatest concentrations recorded. In reply, Daisley 

 (1957) made the sound point that Droop had allowed only for 

 the standing crop and not for overall production. Further, ade- 

 quate allowance cannot as yet be made for the relevant parts 

 played by free B12 and bound B12 in this argument (Daisley, 1959) 

 although we are acquiring many clues as to the various needs for 

 B12 and its analogs and as to substitutions for these (Droop el al., 

 1959). We are as yet some way from a final answer, but we do know 

 that B12 is produced and its availability varies, while many plank- 

 ton algae either need it or can benefit from it (e.g., Provasoli, 1958). 



