522 
It is noticeable that Spoon River carries the largest amount 
of matter in suspension, both absolutely and relatively, as 
shown by the high total residue on evaporation (522.3 to 367.5 
and 268.9) and by the smallest amount of the residue in solu- 
tion (167.1 to 304.1 and 248.2). This is further shown by the 
fact that the solids removed by the army filter in Spoon River 
average 1,755 cubic centimeters per cubic meter to only 592 in 
the same year in the Illinois. The large amount of organic 
matter undecayed and undissolved, and therefore not available 
for the support of the plankton, is partially indicated by the 
high oxygen consumed (14.1 to 10.4 and 5.9), the high albumi- 
noid ammonia (.60 to .48 and .25), and the high total organic 
nitrogen (1.29 to 1.03 and .61), when considered in conjunction 
with the small amount of residue in solution. On the other 
hand, the waters of Spoon River are quite deficient in forms of 
nitrogen more available for the phytoplankton, the free am- 
monia (.24), nitrites (.039), and nitrates (1.01) being in each 
case less than in the Illinois (.86, .147, and 1.58), while the 
chlorine (3.8), an index of sewage contamination, is less than 
a fifth of that in the channel (21.6). 
Spoon River has therefore great resources, in so far as or- 
ganic matters and the products of their decay are concerned, 
for the support of the plankton. Not all of the matter is in 
solution for immediate utilization, but there is still sufficient 
for a large plankton development, time for which has not been 
allowed in the tributary stream. The immediate effect of the 
access of the contributions of Spoon River to the channel is, 
in the average, a dilution of its inorganic nitrogen per m.° of 
water, which is in some unknown measure made good by the 
contributions of silt, in part of organic origin. The net result 
is, of course, a large addition to the total resources of the chan- 
nel waters available for the present and future development of 
the plankton. 
The amount of nitrogen in its several forms which Spoon 
River carries is not small as rivers go, for this stream drains a 
plain unsurpassed in fertility by any other part of the catch- 
