156 Information Storage and Neural Control 



to front. The downward sloping represents the attenuation of 

 photosynthesis with increased depth of suspension due to decreased 

 illumination. The curve of Figure 6 is the locus obtained on this 

 surface by connecting the points (2,2,4.61), (6,6,1.46), and (lO,10, 

 0.85). Now view the surface from left to right. This gives photosyn- 

 thesis as a function of collection depth. Regardless of the depth of 

 suspension, the populations collected at 2 ft. always photosyn- 

 thesized more than those obtained from 6 and 10 ft.; the latter 

 samples appear to give very similar results. These relationships 

 indicate that the organisms taken from deeper layers of the water 

 column have less capacity for photosynthesis than those which 

 normally occupy the surface waters. This may be a reflection of 

 the fact that the deeper plankters are senescent and sinking; 

 microscopic examination usually revealed the surface organisms 

 to be far more active in swimming than their counterparts from 

 below. 



Consider now the thermodynamic efficiency of photosynthesis 

 as reflected by the ratio of mean photosynthesis per mean illumi- 

 nance at each depth. These data are presented in Figure 9. The 

 surface generated is concave "upward, slants upward approaching 

 the viewer and toward the left, and rises sharply on the right in 

 front. Studying from back to front first, we observe that photo- 

 synthetic efficiency increases with depth of suspension, hence with 

 diminished light intensity. This result is in accord with the photo- 

 synthesis literature (33). Now studying the surface from left to 

 right, we observe that plankters living nearer the surface are 

 generally more efficient in light utilization when compared at the 

 same suspension depths with those from deeper layers, except that 

 organisms collected from 10 ft. appear to be almost as efficient 

 as those from 2 ft. when both are suspended at the deeper level. 

 In general, then, the relationships of Figure 9 are consistent with 

 those of Figure 8 in denoting greater productive capacity of surface 

 populations compared to those from farther down. The observation 

 that efficiency increases as light decreases can be interpreted to 

 be adaptively significant in respect to the goal of biomass maxi- 

 mization. The extent of this dark-adaptability under natural 

 conditions is emphasized by comparing efficiencies of the popu- 

 lations at the depths they naturally occupy. Thus the points (2,2, 



