

ALGAL FLORA OP THE MISSOURI BOTANICAL GARDEN. 31 



vegetative state which lived through the winter in the lagoon 

 compared with that of the upper pond and stream was found 

 to be badly beaten by the wave motion. The pond on the 

 south and west side becomes abruptly deep. The prevailing 

 winds during the growing season are in a southerly direc- 

 tion. These combined factors seem to make the shallow 

 east and north side a more valuable field for algal forms 

 which are practically absent from the west side except at the 

 northwest rocky dam which separates the lagoon from the 

 overflow stream. Here on the rocks is a group which must 

 adapt itself to the wave motion and rise and fall of the water 

 level which is variable within a range of 6-8 inches. 



The lagoon, probably due to the fact that it is a larger 

 body of water with more variability of habitat shows less 

 connection between groups. On the deep south and west 

 shores only a few strands of Oedogonium were noted. On 

 the shallow east side, abundant Oedogonium, apparently the 

 same species as that in the Fountain pond and some Spiro- 

 gyra were present. On the mud at the north end, in March 

 for a brief period, a thick film of Chlamydomonas was seen. 

 The rock of the dam at the west was the most favorable situ- 

 ation. There a slender Cladophora sp. grew all the year. 

 Spirogyra, Phormidium, Oscillatorias, Desmids, Diatoms and 

 Tetraspora were prominent during parts of the year. The 

 most conspicuous association and the only well-marked one 

 was that of Anabaena Flos-aquae, Clathrocystis aeruginosa 

 var. major, and Oscillatoria Agardhii floating on the water 

 often mixed with quantities of soot when the wind blew the 

 smoke in that direction. (See Anabaena description.) Conju- 



gatae and Cyanophyceae are predominant. 



Arboretum stream. The water from the lagoon after it 



enters the pasture to the northwest contains only some frag- 

 ments of Spirogyra or Oedogonium until it enters the Arbo.- 

 retum. Near the center of the Arboretum the incline be- 

 comes more abrupt than above, the bed is here narrower and 

 rough with bricks and stones. Here Cladophora flourishes. 

 Toward the east side of the Arboretum the bed widens and 



the slope is slight so that the current is sluggish. In this 



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