225 
furnishes a large part of our phytoplankton of midsummer and 
the bulk of the water-bloom. The experiments of this author have 
shown conclusively that this chlorophyll-bearing 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 become paler. In the 
dark it becomes colorless, and depends entirely (saprophytic) 
upon the dissolved organic 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, alge, 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 Euglena, viz., viridis, 
sanguinea, deses, acus, spirogyra, and gracilis. I have noted it 
also to a very marked degree in Chlamydomonas, Carteria, 
Trachelomonas, and Lepocinclis. It has been less pronounced in 
the Peridinide, in Mallomonas, and Dinobryon. Among the 
diatoms the most striking instances occur among the typical lim- 
netic forms, such as Synedra, Melosira, and Asterionella, Inthe 
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. 
