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PLANKTON ALG OF LAKE ERIE. : 373 
a partial list is added of the alge occurring in the plankton, though this is by no 
means complete, as comparatively little time was given to the determination of the 
Diatoms. The material was merely preserved for future examination. The 
determination of the Desmids was mainly left to Mr. A. J. Pieters, who has given a 
list of this family. (Pieters 01.) A number of the Cyanophycece also, which are 
common in the plankton, have not been determined. These are minute gelatinous 
forms occurring as flocculent masses in the water, and though the structure of the 
cells is constant, the form of the colony is more or less variable, depending 
apparently on the age of the colony and the kind and amount of nutritive sub- 
stanees in the water. To make an accurate list of these would require careful 
comparison and a more perfect knowledge of their life conditions than we now have. 
Undoubtedly many of them are undescribed species. Though the list of Chloro- 
phycee here given is fuller than that of other classes, it is by no means complete. 
Some unrecognized forms were met with where attempts at cultivation failed, due 
to inappropriate culture conditions, and as a result classification could not be made. 
In the examination of fresh plankton material, the more conspicuous forms were 
easily detected, but there were always a number of minute forms, such as Chlorella, 
Chlorosphera, and Chlamydomonas, which easily escaped notice, or, if observed, 
they appeared as single green cells which could not be identified. That these might 
be taken account of, and not be altogether overlooked, large cultures were started 
from the fresh plankton, and in these cultures developed many such forms which 
had escaped observation in the examination of the fresh material. Some of these 
were isolated from all other forms of alge and their development studied. It is 
believed, however, that farther study in this line will give many additional species 
and many interesting biological facts, for as yet but few of these larger cultures 
have been thoroughly examined and the species determined. 
For the names of species, where a detailed study is not given, the determination 
is based on the simple descriptions of other authors. The list is given, however, 
only as a temporary guide to the forms present, for it is believed that new methods 
of investigation, when applied to the development of even some of the best recog- 
nized genera, will change the nomenclature considerably. Some forms which have 
been classed together may prove to be distinct species, and possibly others which 
show variation should be combined to form one species. 
In the physiological work done on these forms, by far the greatest amount of 
attention has been given to the subject of nutrition and culture media. Tempera- 
ture is of less importance, for relatively great variations do not seem to affect them. 
The water in the natural condition never reaches a temperature so high as to kill 
them, and low temperature—even freezing, at least in sone cases—does not end their 
existence, but seems to affect them mainly in reducing their rate of increase. The 
degree of light, too, in which they can live would seem to vary largely, as they are 
often found at considerable depth, as well as at the surface. The belief of many 
recent investigators that algee with chromatophores may make use of both organic 
and inorganic substances in their nutrition, is supported by the experiments of 
Artari 701 and Knorrich ’01, both of whom found that the alge used in experi- 
mentation thrived much better when organic substances were present in addition to 
the inorganic. Artari even found that at least certain forms could live and remain 
green in total darkness. . 
It has been the experience of the writer that great variation exists among 
