150 



NIELSEN 



CHAP. 7 



(a) 



L. 



(b) 

 Fig. 10. An apparatus for filtering plankton by pressure 



were not significantly different from those of corresponding samples suspended 

 simultaneously at the normal depth in the sea. Fig. 1 1 presents such a simulated 

 in situ experiment. Menzel and Ryther (1960) have used this method for 

 measuring the annual variation of primary production near Bermuda in the 

 Atlantic. A simple device for agitating the bottles during such experiments has 

 not yet been invented. However, in areas with habitually rough weather, it is 

 sufficient to put glass pearls into the bottles, which are placed horizontally. 



