225 



furnishes a large part of our phytoplankton of midsummer and 

 the Inilk of the water-bloom. The ex])eriments of this author have 

 shown conclusively that this chlorophyll-l)earing organism is 

 usually autotrophic (holophytic) in the light and in the ab- 

 sence of abundant organic nitrogenous matters in solution, and 

 under these conditions its chromatophores are a bright green. 

 When organic nitrogenous matters in solution are abundant 

 the organism becomes mixotrophic (half saprophytic) even in 

 the light, and its chromatophores may liecome paler. In the 

 dark it becomes colorless, and depends entirely (saprophytic) 

 upon the dissolved orfjanic nitrogen for its growth and multi- 

 plication. 



The waters of the Illinois River and its backwaters are 

 unusually turbid, thus excluding more than the usual amount 

 of light. The plankton of this environment is rich in species 

 and individuals of flagellates, alga?, and diatoms, many of 

 which exhibit this tendency to become paler. This I have 

 noticed repeatedly in the examination of the living plankton, 

 and to some extent in material preserved in formalin-alcohol. 

 It has occurred in the several species of EugJena, viz., viridis, 

 sumju'uiea, denes, aciis, spirogyra, and gyac'dis. 1 have noted it 

 also to a very marked degree in Chlamydomonas, Carferia, 

 Trachelomonas, and LepocincUs. It has been less pronounced in 

 the Peridiru'da', in Malloniouas, and Dinohrgoii. Among the 

 diatoms the most striking instances occur among the typical lim- 

 netic forms, such as Sgnedra, Melosira, and Aster wnella. In the 

 light of Zumstein's results, and in view of the chemical data exhib- 

 iting an absence of proportional correlation between the move- 

 ments of the organic nitrogen and the fluctuations in the volume 

 of the plankton, and of the frequent occurrence in our waters of 

 colorless individuals of chlorophyll-bearing species, it seems 

 that we are justified in assuming that the flux of nitrogenous 

 matter involved in the plankton changes lies to some appreci- 

 able and as yet undetermined extent within the range of sub- 

 stances included within the dissolved and suspended nitroge- 

 nous matter of the water. 



