306 
swept away all but a vestige of the rich plankton of the earlier 
weeks. The amount remaining was so small that its quantita- 
tive changes were swamped in the errors of the volumetric 
method and silt estimation. The large amount of silt carried 
in this and subsequent floods of the winter is due to the fact 
that bottom-lands and fields covered with a rich vegetation were 
now submerged for the first time in two years (Pl. VII.), and 
vast quantities of debris from this region and tributary streams 
now entered channel waters. 
In comparison with other years December in 1895 is, in 
spite of its fortnight of flood, the most productive December 
recorded (see table on p. 292), averaging 1.14 cm’ to .76 in 1896, 
.56 in 1897, and .99 in 1898. It shares the large development 
of the preceding month, and with it presents the most marked 
late autumnal development in channel waters, though falling 
far below the production of some of the permanent backwaters 
in this and other years in this season. The unusually stable 
hydrographic conditions in the river doubtless contribute in 
large measure to this exceptional development. That low tem- 
peratures aione do not prevent the development of a large win- 
ter plankton is apparent from this December development of 
2.6 cm.® per m.’ and 11.1 cm.’ per square meter at temperatures 
but little above 32°. 
The year 1895 as a whole may be summed up as one of mid- 
winter stagnation followed by excessive spring and early sum- 
mer development of the channel plankton, of midsummer and 
equinoctial floods, which check development at that season, of 
stable autumnal conditions and exceptional production in late 
autumn, and of catastrophic reduction by flood to a minimum. 
As a whole the year was one of exceptionally heavy production 
when expressed in terms of plankton per cubic meter. This is 
seen in the high average—3.22 cm.’ of all catches, 5.31 em.* of 
monthly averages. When total production is considered it may 
be that the decreased volume of water at the time of the maxi- 
mum in the low water of June will at least counterbalance the 
excess per cubic meter, and that the total production will not 
