146 Lake Maxinkiickee, Physical and Biological Survey 



lated along- the shore in sheltered places, usually in rather small 

 amounts, however. It was only occasionally collected and only a 

 few notes were made concerning it. Anabsena was almost always 

 present, but apparently did not make up the main mass. 



During the summer of 1906 — a calm, dry summer — the plank- 

 ton-scum was present in unusual abundance and was made up 

 chiefly of this species. It was frequently examined, so that the 

 species was under pretty continuous observation for that year, 

 and its history is nearly the same as that of the scum in g-eneral. 



On July 30, 1906, on a trip to Norris Inlet it was noticed that 

 the water of that region was full of diffused minute blue-green 

 flecks. Hauls were made with the towing-net but nothing was ob- 

 tained but duckweeds. The fine, flocculent material was probably 

 Anabsena. It was found later that it readily strained through the 

 finest towing-net on hand. 



The next day the water of the lake seemed full of suspended 

 algae. A towing was taken in the morning from Long Point (Chad- 

 wick's) to the office, and many entomostraca were taken, but the 

 small algge escaped. At noon the water by the office seemed very 

 full of the same material and dips were taken with the fine net, but 

 nothing- much was obtained ; the fine algse again escaped. In the 

 afternoon of the same day a fine blue scum, the first of the year, 

 was observed in a minnow-box. This was secured by dipping 

 with a vial, and proved to be Anab?ena. About 2 o'clock the scum 

 was quite pronounced, first in a ditch-like artificial channel (boat 

 slip) , dug into the shore in the south side of Outlet Bay, the excava- 

 tion being 15 or 20 feet wide, and 80 to 100 feet long, forming a 

 calm, sheltered harbor. Somewhat later in the same day, the scum 

 gathered thickly in front of the office, and was collected and 

 examined. 



In this particular instance the appearance was somewhat dif- 

 ferent from usual ; the scum was composed of minute dark green 

 balls in active motion, somewhat resembling minute colonies of 

 Volvox except for the darker color. On examination the material 

 was found to be composed of dense balls of tangled Anabaena fila- 

 ments, almost every ball surrounded by a halo of attached Vorti- 

 cellas, the contractions of which had caused the motions of the 

 mass. The appearance of the balls with the radiating, jerking- 

 Vorticellas was quite striking. 



From this time on until late autumn, scum composed mainly of 

 Anabsena, was present in considerable quantities somewhere along 

 shore every calm day, and on some days covered the whole lake 

 more or less completely (August 6 and August 7). It frequently 



