1922] Allen: Siudies on Marine Phytoplcmkton at La Jolla 333 



December. A diatom jml.se at the middle of September was 

 almost precisely coincident with a dinoflagellate pulse and there was 

 partial coincidence of pulses of the two groups just after the middle 

 of December. The fact that out of four chances for coincidence there 

 were two close approximations to coincidence of pulses gives strong 

 indication that both groups of organisms are often favored by the 

 same stimuli to production, hence the idea that they may be mutually 

 exclusive may seem unwarranted. 



But an examination of the evidence from swarms shows other 

 possibilities. A swarm may be arbitrarily defined for present pur- 

 poses as a close aggregation of relatively large or even vast numbers 

 of organisms of a certain group. Although what I have called a pulse 

 may be (at least in some cases) due to the slow drift passing of an 

 enormous swarm which occupies an area of several miles, I think we 

 may confine present discussion to evidence of small swarms. This 

 evidence consists merely in a conspicuous large catch found between 

 much smaller catches, mostly less than one-third as large. Swarms 

 identified in this way were, as might be generally expected, much 

 more numerous than pulses in spite of the fact that nearness to shore 

 made it probable that many swarms would be dispersed by the great 

 disturbance in shallow waters. In the four months there were fourteen 

 swarms of diatoms and fifteen swarms of dinoflagellates. Out of the 

 fourteen chances for coincidence of swarms of the two groups only 

 four actually occurred, a fact which might lead one to think the two 

 groups somewhat deterrent to each other. 



Not only does the evidence of pulses and swarms raise some in- 

 teresting questions as to the interrelationship of the two great groups 

 of synthetic organisms; it also has direct bearing on the perennial 

 postulate that marine organisms are uniformly distributed through 

 considerable areas of marine waters. The occurrence of pulses and 

 swarms such as those just mentioned certainly tends strongly to 

 contradict this assumption. 



Further evidence tending to such contradiction appears in what, 

 for lack of a better term, I may call skips. In the present connection 

 a skip means a single strongly marked reduction in numbers in a way 

 similar to that in which a strong increase is considered to indicate a 

 swarm. In the four months, diatoms showed ten skips and dino- 

 flagellates five, no two of which coincided. Surely a marked lack of 

 organisms in a catch as compared with a catch twelve hours before 

 and another twelve hours after gives good reason to suspect that 



