54 MINNESOTA BOTANICAL STUDIES. 



five feet wide, from the shore out into the lake, was almost 

 thickened by the presence of a great number of colonies or 

 bundles of this plant. This scum being suspected as the source 

 of danger, a temporary fence was put up to prevent the cattle 

 from drinking out of the lake. After that, none of the cattle 

 died or showed symptoms of being poisoned. In a letter 

 describing the circumstances, Professor Ballard states that he is 

 convinced that the death of the cattle was due to the drinking 

 of the lake water, either because of the poisonous characters of 

 the algae, or what seems more likely, because of the stagnant 

 condition of the water which made the growth of the algae 

 possible. 



On October 13, 1901, the writer collected some "water 

 bloom " on the shores of Lake Minnetonka at Spring Park. 

 The water here did not seem to be very deep for some distance 

 from the shore. Neither was there a clean sandy bottom in the 

 vicinity. Bulrushes grew abundantly in places and there were 

 present some smaller water plants. The water of the lake was 

 quite fresh and clear. 



The algal scum was gathered at a" few places along the shore 

 by a gentle land-ward breeze. It had a pale bluish-green color 

 resembling a mixed paint of that color. Microscopic examina- 

 tion showed the scum to be made up of two species of Anabcena, 

 A. fos-aquce (Lyngb.) Breb. {PL XIV., Fig. 3) and A. cir- 

 cinalis (Kuetz.) Rabenh. {PL XIV., Fig. 2). 



On October 24 another collection was made at the same spot. 

 The scum was about the same in quantity, but was of a grayish- 

 brown color, slightly tinged with blue-green. It was more 

 slimy to the touch. It had an odor similar to mouldy grass or 

 hay. Under the microscope it was seen that this difference was 

 probably due to the presence of a much larger number of gonidia 

 or reproductive bodies than had been found in the previous 

 collection. 



To the naked eye this scum appeared to be simply a shapeless 

 mass, but examined with the microscope it was found to consist 

 of innumerable filaments, resembling strings of beads. Each 

 of these filaments or trichomes was composed of a number of 

 somewhat spherical pseudocysts, almost uniform in size and 

 shape. Each pseudocyst was filled with a dense, finely gran- 

 ular protoplasm. At intervals in the trichome were seen hetero- 

 cysts, larger than the pseudocysts, with a more distinct wall and 



