452 
to stable hydrographic conditions, abrupt changes being limited 
to less than 8 weeks in the year (Pl. [X.), and to low water 
and consequent slackening in the channel with increase of time 
PLANKTON PRODUCTION IN 1895.* 
Station Feb. Apr. May | June July Aug. 
OOM so rnadce osno owes wae —| 0.01)-— Giediellon [1 3°. 42|+| 9.33/-+] 4.03 
Ouiver ake ee sorcerer eee || OCs = 3.00]. .|.. «![acl- oie) 2/<i| =|). 0837 a Nba 
Dogfish Wakes. to seas 5 Re, 740) nallsiaodc =| 0; ‘12\-+ 2.99|--| I.11 
Blag bake: 02 -ckuewceserers avatsh| Si] beeches [ell eres te lee aes olla ee ee 
Mhompsonis Wakiere cect etree ren aa! 28. 20\-+\61. 44\- = ‘9. “q2lh Ae 83 —| 3.09 
Mean of 
Station Sept. Oct. Nov. Dec. monthly 
Averages 
UInOISHRIV.e ren eee ey ee —| 1.52 |—| 0.57 |+] 3.02 |+| 1.14 |+] 5.91 
Quiver taken. cacmscccce cerns +] 0.94 |—| 0.13 |—| 0.05 |—} 0.46 |—| 0.65 
Dogfish Bakes. 66: csiee oe yes pote Be ESe ae |) 2520 tol SOs [1-15 32) |= 
Puleip alae sy ses creer scree ey eee US tyes . |+157.76 |+] 14.40 |+] 4.82 |+] 25.66 
MhompsoniseUa kena creer —| 3.58 |—| 3.15 I—]| 5.07 !—| 1.00 +] 13.31 
*The minus sign signifies below average and the plus sign above. 
for the breeding of the plankton. The larger amounts of plank- 
ton were found only during stable conditions, and floods inva- 
riably depleted the volume of the plankton. These periods of 
stable conditions occur in summer and late autumn, and we 
find the plankton content at such times 3- to 30- fold that in 
contiguous flood conditions. In the river the monthly produc- 
tion exceeds the monthly average for our records in 5 out of 
the 9 months represented, the exceptions being February, when 
stagnation under the ice prevailed, April, a vernal period of 
low water without overflow, September, a month of repeated 
floods, and October, when an unusually early decline in temper- 
ature occurs. 
The stable conditions which attend low water thus favor 
the increase in the plankton content per m.*, though by reason 
of the lower levels and slackened current the total volume pro- 
duced in the stream asa whole must be greatly diminished by 
such hydrographic conditions. 
The results of this low-water year upon production in Quiv- 
er Lake (Pl. XXX.) are as a whole diametrically opposite to 
those in the river. Here in the lake, production falls below 
