FRESH WATER ECOLOGY; SOIL ALGAE 



365 



Phase 



Autumn 

 Winter 

 Early spring 

 Late spring 

 Summer 



Dominants 



Closterium, Englena, Oedogonium 



Spirogyra spp. 



Spirogyra sp. 



Spirogyra, Euglena, Oedogonium 



No one species 



In another pond somewhat different phases were recorded : 

 Phase Dominants 



Autumn Oedogonium, Chaetophora 



Winter Vaucheria 



Late spring Oedogonium, Pleurococcus 



Summer Chaetophora 



These observations should be compared with those from the 

 Harpenden pool, and it will be seen that although the spring phases 

 are essentially similar with either Spirogyra or Oedogonium, never- 

 theless there are great differences. The two ponds described above 

 also possessed floras that were essentially different and they must 

 therefore be regarded as containing two separate associations. 

 Furthermore, the same worker found that a sudden change in the 

 external conditions checked the growth of an alga and often re- 

 sulted in the development of a resting stage or else of sexual organs ; 



1906 SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. JMAY JUNE \}^^^^^- 

 20 "^Ts 9~7r TT? T 17 I H I 15 3 15 I 14 I 13 I 15 I 



VERY 

 ABUND. 



ABUND. 



RATHER 

 ABUND. 



RATHER 

 RARE 



RARE 



VERY 

 RARE 



Q-' Water 



Z 



h" Air 



T — I — I — r-] — I — r— 1 — I — I — r 



OEDOGONIUM 

 CRYPTOPORUM 



T — I — I — I — I — r— I — r— 1 — I — r 



/•'"■-N, SPIROGYRA 

 / ^'^.JSIITIDA 



\ EUGLENA 



SPIROGYRA/ 

 VARIANS / 



it 

 f* 



_J I I — L 



-— -"^ ♦ r\ n<;TFRii im 



CLOSTERIUM 

 ACEROSUM 



11/11 I \ t I 1 / i I I'^-L I I I *^M 



'C 29 18 20 20 4 I 10 7 6 16 12 12 20 8 24 31 23 33 30 28 35 



°C 28 20 15 13 7 5 9 7 I 9 12 19 22 II 24 28 16 29 24 24 33 



Fig 200 Abundance and frequencies of the most important algae 

 in a pond near Indiana University from 1906 to 1907. (After 



Brown.) 



