THE PEECIPITATION OF CALCIUM CARBONATE IN THE SEA. 481 



At present no really reliable and accurate chemical method of 

 estimating the combined Nitrogen in sea-water exists, hence the above 

 theory cannot be directly put to the test. On the other hand, the 

 existence of denitrifying bacteria in Temperate waters has long been 

 known, and it would seem a fair deduction that should this bacterial 

 destruction of Nitrates take place with greater intensity and complete- 

 ness in Tropical than Temperate waters, an explanation of the relative 

 scarcity of phyto-plankton in the former would be offered. This 

 suggestion was first made by Brandt (2) in 1901, and is universally 

 known as " Brandt's hypothesis." He enunciated it as follows : — 



" If the denitrifying bacteria of the sea, like the closely-investigated 

 denitrifying bacteria of the land, develop a strongly disturbing activity 

 at higher temperatures, only a relatively small production (of phyto- 

 plankton) would take place in the warm seas in spite of mucli more 

 favourable conditions, according to the law of the minimum, owing to 

 the great disturbance amongst the indispensable food substance ; 

 whilst, in the cold seas, more nitrogen compounds would be at the 

 disposal of the producers owing to the retardation or suppression of 

 the disturbing process." {From the published English translation.) 



The presence of denitrifying bacteria has been demonstrated in Kiel 

 Bay by Baur (1), along the Dutch coast by Gran (9), in the open 

 waters of the North Sea and Baltic by Feitel (7) and Brandt (2 and 8), 

 and in 1909 I identified several of the species described by Gran in 

 samples of water obtained from the Western part of the English 

 Channel. All these denitrifying species have a higher temperature 

 optimum than that of their natural environment, and this is obviously 

 a point strongly in favour of Brandt's hypothesis. 



The chief difficulty in the way of putting the hypothesis directly to 

 proof lies in the fact that at present no accurate method of deter- 

 mining the Nitrate contents of sea-water exists, and hence it is 

 impossible to correlate quantitative plankton observations with direct 

 analysis of the amount of combined Nitrogen present in sea-water in 

 different localities. Much valuable work on this subject has been 

 done by Eaben (15), but he states that his error in control experiments 

 averages over 30%. An exhaustive study (as yet unpublished) of all 

 the methods of estimating combined Nitrogen in sea-water, as given 

 by various investigators, has been made by Mr. D. J. Matthews, 

 Hydrographer to the Marine Biological Association of the United 

 Kingdom, and he has come to the conclusion that the limits of error 

 in all these methods are so large as to make them quite unreliable. 

 Since chemical methods are at present inadequate to give evidence on 



