NOVEMBEB 5, 1900] 



SCIENCE 



647 



river plankton, however, its quantity was 

 larger than that which has been obtained from 

 the upper strata of the Atlantic Ocean. 



The phytoplanlvton consisted chiefly of algse 

 and the zooplankton of Protozoa, Eotifera 

 and Entomostraca. Eelatively the plants out- 

 numbered the animals nearly five to one. For 

 each of the Cladocera, there were 7 Copepoda, 

 95 Rotifera, 18,000 Protozoa and 86,000 plants. 

 This large number of plants would furnish an 

 abundant supply of food for the zooplankton. 



By far the greater portion of the paper con- 

 sists of a detailed discussion of the statistical 

 data pertaining to the various constituent 

 organisms, but space will permit the consider- 

 ation of only the most important of the larger 

 groups. Bacteriacese were found throughout 

 the year, but they reached their maximum 

 development in the winter from December to 

 January. They sometimes became a serious 

 menace to the fishing industry as they col- 

 lected on the fyke nets in such masses that 

 their weight and resistance to the current 

 would break the nets. 



The Myxophycese also contributed to the 

 phytoplankton throughout the year. Quanti- 

 tatively this group was not so important as 

 some of the others, owing to the small size 

 of its most numerous member, Microcystis. 

 Rivularia, Gloeotrichia and Aphanizomenon, 

 •which occur so generally in lakes, were not 

 found in this fluviatile plankton. The Chloro- 

 phycero were well represented both in species 

 and individuals and showed evidences of their 

 adaptation to the whole range of temperature 

 changes. The group as a whole exhibited 

 maximum periods at approximately monthly 

 intervals. Bacillariaceae were found in every 

 collection and their seasonal distribution was 

 substantially repeated from year to year. The 

 chief maxima were found in April-May and in 

 November-December, with smaller maxima 

 and minima intervening. 



All the collections contained large numbers 

 of Protozoa. The Mastigophora, which con- 

 sisted chiefly of chlorophyll-bearing Protozoa, 

 ■were found at all seasons of the year, but four 

 fifths of them came between the first of April 

 and the last of September, or during the sea- 

 son of growth for land flora. 



While Rotifera were obtained at all seasons 

 the number was uniformly low in winter. 

 They showed great fluctuations at other sea- 

 sons. There was an apparent tendency, how- 

 ever, for a vernal and an autumnal maximum. 

 With three exceptions no maxima of any con- 

 siderable amplitude were found when the tem- 

 perature of the channel water was below 

 15.5° C. 



The Entomostraca as a group were repre- 

 sented in all collections. The minimum num- 

 ber was found in mid-winter and the maxi- 

 mum for the year in April and May. During 

 the remainder of the year, there was usually a 

 series of recurrent maxima and minima which 

 generally coincided with or approximated such 

 periods in the other plankton organisms and 

 often showed correlations in amplitude. 



Cladocera were noted every month of the 

 year, but they did not appear in ten of the 

 collections. The minimum numbers were 

 found during the period of minimum temper- 

 atures and the total varied more or less with 

 the hydrographic changes. The Copepoda 

 were, on an average, about five times as nu- 

 merous as the Cladocera. They were peren- 

 nial and had a major maximum in April-May 

 with an occasional autumnal maximum of 

 equal or greater proportions. By far the 

 greater proportion of the Copepoda were 

 young, 78 per cent, being nauplii of Cyclops 

 and Diaptotnus, and 13 per cent, immature 

 Cyclops. 



In the concluding chapter. Professor Kofoid 

 states that one of the most obvious conclu- 

 sions of his detailed study is that the plank- 

 ton production was fundamentally rhythmic 

 or periodic in character, viewed either in its 

 constituent elements or as a whole. The ex- 

 ceptions to this rhythm were usually the ad- 

 ventitious forms. The cause of the periodic- 

 ity was not clearly revealed. It was not 

 correlated with the physical and chemical con- 

 ditions of the water. The duration interval 

 of the rhythms averaged approximately that 

 of the lunar month, but showed considerable 

 variations, as might naturally be expected, 

 owing to the very large number of environ- 

 mental factors involved. 



