403 



approximate collections show this agreement. A comparison 

 of Plates X., XXVIL, and XXXI. with XXXVII., will show 

 that much of this disagreement is due to slight variations in the 

 positions of the apices of the several pulses in the different 

 localities. In each locality we can trace three diminishing 

 pulses in this period, pulses, moreover, which have much in 

 common, barring variations in amplitude and time of culmi- 

 nation. Their similarity is greater than the 58 per cent, of agree- 

 ment would seem to indicate. 



The most marked difference between the production in the 

 river and in Thompson's Lake, as has been shown, lies in the 

 amplitude of the pulses, which in the river never attain the 

 height that they do in the lake. A part of this contrast is due 

 to the fact that pulses of production are sometimes flushed out 

 by floods in the channel while they continue to a normal cul- 

 mination in lake waters, as, for example, the vernal pulse which 

 culminates in the lake May 2. Similarly, in the flood of the last 

 of May and July the plankton content is suddenly depleted in the 

 channel waters, while the rising pulse continues to a later and 

 much higher culmination in the lake. 



1897. 



(Table VIII., XIII.; PI. XXXVIII., L.) 



There are 18 collections in this year, at monthly intervals 

 till July, and thereafter approximately every fortnight . The 

 average annual production this year, 10.43 cm. 3 per m. 3 is the 

 largest recorded for this body of water, and is due to the exces- 

 sive development in the low-water period, August-November, 

 which reached an amplitude (35.35) over threefold that de- 

 tected in the vernal pulse (10.38). (PI. XXXVIII.) 



The hydrographic conditions are very different from those 

 of the previous year, and change profoundly the relationship 

 of the lake and river. As will be seen on Plate XXXVIII. , the 

 river levels were above 6 ft. from the beginning of the year 

 until June 6, and thereafter from the 25th until July 15, a total 

 of 175 days in which the lake received water through the 



