— 85 - 



correspond ing- figures in the last three colnmns of the table on 

 p. 84. We think the évidence is sufficient to indicate that the 

 time of occurrence and the durationof the maximum (AEuglena 

 in the différent years dépends directly on the enrichment of the 

 water by the remains of the decaying filamentous flora. 



In the autumn months a somewhat similar enrichment of the 

 water will take place at the expense of the dying Phanero- 

 gamic végétation, but tins decays less rapidly than do the simple 

 Algae, and the solution of organic matter by the water will 

 go on more slowly owing to the lower température. Neverthe- 

 less an addition of soluble organic substance is bound to take 

 place at this time and will account for the autumn-phase exhib- 

 ited by the Euglena in 1906 and for its persistence in some 

 quantity until November in 1907 and 1908. Possibly a richer 

 development at this time inspite of the présence of organic sub- 

 stance is prevented by the insuffîcient sunshine. 



Table to show occurrence of Flagellata in Barton's pond, 



1006-1909 <*>. 



The two species of Trachelomonas found in the pond show 

 a rather différent frequency table. T. hispida is always rare 

 during the first half of the year, becoming commoner in May 



(1) For explanation of, symliols, see ibotnote 1 on p. .">4. In the table of 

 occurrence of Trachelomonas the more abunrlant species in each month is 

 indicated by a V (for volvocina) and an H (for hispida). Where no such letters 

 are added the two species were equally abundant. 



