221 
and its interpretation, in many cases at least, becomes probable, 
if not, indeed, certain. 
In the first place it may be noted that the fluctuations of 
the plankton are not paralleled by proportionately great move- 
ments in the total nitrogenous substances in the water which 
enter largely into their composition. For example, the spring 
maximum of the plankton is accompanied by no such wave in 
thesesubstances. Indeed,aslightripple of depression seems to be 
the only concomitant fluctuation. Even granting a large mar- 
gin because of the absence of a common unit of measurement, 
it remains apparent that the fluctuations of the substances in 
question and of the plankton are not proportional. A single 
illustration, found in the spring maximum in Quiver Lake in 
1898 (Pl. XLIX.), will suffice to make this point clear. The 
following table, drawn from Table XIIL., gives the amounts of 
plankton and of the several forms of nitrogen present before 
QUIVER LAKE. 
Date Free Albuminoid} Organic 
1898 Ammonia | Ammonia | Nitrogen Nitrites | Nitrates | Plankton 
Aprile igs .046 44 1.01 .033 65 | 103 
MESY Slesooneoat ,092 3 82 .022 | 35 | 42.14 
IMMER 7 IO \gendaoe .05 .48 .98 O15 a | : 4.7 
—_ —— — — — I — 
Per cent. of Change. 
April 19 to ior. | Pe Lene | SE cn = el as aS 
May 3...... +100 ee alg — 33% — 46 +3991 
(April 19), during (May 3), and after (May 11) the plankton 
wave, and the extent of the change, in per cent., of the amount 
present on the 19th which each exhibits. The plankton rises 
from 1.03 cm.’ per m.* to 42.14, falling subsequently to 4.70 and 
1.97. This is an increase of 3991 per cent. No one of the ni- 
trogenous substances in the table exhibits a change exceeding 
100 per cent.,and the average change is only 45 per cent. In 
this case the change in plankton is eighty-eight times as great 
as that in the average of all forms of nitrogen, assuming, of 
course, that the units of measurement are comparable, 
