PLANKTON OF THE GULF OF MAINE 479 
ently requires “ some specific substance present in minute quantity in the natural 
sea water” (E. J. Allen, 1914, p. 439), but not in the artificial. 
Fritz (1921a), experimenting in the culture of diatoms at St. Andrews, New 
Brunswick, found that Melosira hyperborea not only made considerable growth in 
artificial sea water but continued to multiply rapidly in cultures in natural sea water 
long after Thalassiosira nordenskioldi, Chxtoceras debile, and Skeletonema costatum 
became exhausted. Her conclusion that the persistence of Melosira is permitted 
by its independence of some substances which the other forms required but soon 
exhausted seems justified. 
Suggestive, also, in this co nn ection is Crawshay’s (1915) observation that the 
excretory products of the copepod Calanus jinmarchicus (apparently not, however, 
of Pseudocalanus or Acartia) exert a strong fertilizing action on the diatom genus 
Nitschia; but no such effect followed E. J. Allen’s (1914, p. 429) introduction of 
the crustacean genus Hemimysis, with its faeces, into artificial sea water, which 
proved as barren for diatom growth with as without them. 
Nathansohn (1906) has suggested that the supply of carbonic acid (C0 2 ) may 
temporarily fall below the minimum required for active growth of the phytoplankton, 
a possibility also accepted by Gran (1912, p. 380) ; and Moore’s calculation 88 that 
20,000 to 30,000 tons of carbon are annually converted from inorganic to organic 
form per cubic mile of water in the Irish Sea emphasizes the vast amount which the 
flowerings of diatoms and peridinians utilize. More recent experimentation on the 
dynamics of photosynthesis 89 have shown that when the total available C0 2 has 
been withdrawn from the bicarbonates present in sea water the latter becomes fatally 
alkaline, and since sea water has never been found in this state or even approxi- 
mating it, although many determinations of alkalinity have been made, it is safe to 
conclude that the growth of marine phytoplankton is never prevented by a shortage 
of carbon dioxide. 
The facts outlined above show that the coastal waters of the Gulf of Maine are 
probably more fertile for diatoms in spring than at any other time of year with 
respect to dissolved silica; likewise in nitrogen, one of the other nutrients on which 
this particular group of planktonic plants chiefly depends. The density and state 
of vertical circulation of the water also influence their abundance, both by governing 
the availability of the phosphoric acid and compounds of nitrogen that go into solu- 
tion on the bottom of the sea and by influencing the flotation of the diatoms them- 
selves. 
The influence which the state of circulation of the water exerts on the seasonal 
abundance of diatoms seems first to have been fully appreciated by Whipple (1905, 
p. 103) for fresh water, for which it is now accepted generally. Briefly it is as follows : 
During periods of stagnation (that is, when there is no vertical circulation) the 
bottom waters of lakes are the seat of active decomposition of organic matter, with 
consequent increase of ammonia and solution of inorganic substances. When 
vertical circulation recommences this “foul” water is brought to the surface, where, 
88 Quoted from Herdman (1920 and 1923). 
^Especially Osterhout and Haas (1918); Moore, Prideaux, and Herdman (1915); Moore, Whitley, and Webster (1921) 
