1920] Allen: Plankton of the San Joaquin River 33 



Ciliata 236, 64, and 48 to 1, Mastigophora 927, 361, and 292 to 1. 

 Cladocera are outnumbered by plants 6540, 6090, and 4555 to 1. 

 Diatoms are responsible for most of this with 5652, 5640, and 2314 

 to 1. Schizophyceae appear at 400, 185, and 217 to 1 and Chloro- 

 phyeeae 452, 214, and 198 to 1. 



The most striking features of these results when compared with 

 those of Kofoid (1908) are two in number. First, there is the re- 

 markable number of Copepoda in Station I. Second, the astonishingly 

 small number of synthetic organisms and of Protozoa at all stations, 

 in proportion to the number of Cladocera. Since Cladocera are almost 

 all caught in the adult stage and since they are almost all retained by 

 the silk net, they present very good ground for comparison of plank- 

 ton catches everywhere. Hence the numbers of Cladocera, the lack 

 in numbers of other organisms and the results of the few, tilter paper 

 catches point conclusively to the fact that the numerical and volu- 

 metric study of plankton calls for absolute filtration, high magnifica- 

 tion and a laborious technique adequately to represent the sources of 

 food, and the interrelations of the organisms of the plankton. 



DETAILED DISCUSSION OF STATISTICS RECORDED BY THE AUTHOR 



Peepatoet 



Tables and plates have been prepared to show in numerical or 

 graphic form the various facts of distribution and occurrence which 

 are or may be reckoned as important. This commentary is intended 

 to elucidate and amplify such records and to serve especially as a 

 guide to the details of observation or conclusion concerning which the 

 writer is certain or uncertain. Averages, when given for each or- 

 ganism in numbers per cubic meter will be given for each station on 

 the basis of 104 collections at Station I, 52 at Station II and 51 at 

 Station III. Averages are only used because there is no other way 

 of making a general numerical comparison in brief form. Tempera- 

 tures, in degree Centigrade, are given both for surface water and 

 for air. While the latter may be unnecessary it was thought that it 

 might help to give an idea of the conditions locally. 



Numbers of planktonts are recorded in units for the same rea- 

 sons of consistency and convenience as those mentioned by Kofoid 

 (1908). There is not the slightest intention to imply fictitious accu- 

 racy by unit expression. Those who prefer can read the record in 

 "round numbers." The writer himself rarely gives any thought to 

 more than the first three figures of a number. 



