386 SECTIONAL TRANSACTIONS.— K. 



The work has been concerned mainly with the relationships of the micro- 

 and macro-flora to the fauna, especially the Trichoptera, Ephemeridae, 

 Mollusca, and Gammarus, both as sources of food and for purposes of 

 protection. 



Methods tending to the encouragement or discouraging of certain forms 

 of life are being studied experimentally. These are discussed, and the 

 further lines of study they suggest are indicated. 



Dr. R. W. Butcher. — The effect of organic effluents on the biological 

 balance in running water. 



Four characters of organic sewage effluents may be considered to react 

 on the biology in running water : (i) Deposition of fine silt ; (2) deoxy- 

 genation of the water ; (3) bringing in of nutrient matter ; (4) the increase 

 or introduction of salts that affect the biology in other ways than nutrition. 



Silt is trapped by masses of plants in swift waters, or deposited in slow 

 waters. This deposit increases the fertility of the river-bed, and helps 

 locally with deoxygenation of the water. 



Deoxygenation of the water affects the fauna much more than the flora. 

 Serious deoxygenation exterminates most of the animals except chironomids 

 and tubificids. Lesser oxygen deficiency increases the fauna of clean and 

 foul mud and reduces considerably the fauna of stony stretches. Although 

 deficiency of oxygen also kills fish, it is not known what is the minimum 

 amount of oxygen in which a fish can survive. 



The extra nutrient matter supplied by organic effluents has a very marked 

 effect on the flora. Sewage fungus is abundant in waters rich in organic 

 matter. Certain algae, such as Cladophora glomerata, Navicula radiosa and 

 Cocconeis placentula, are very abundant when organic matter is present 

 in smaller amounts. 



Other salts contained in sewage that affect the flora and fauna are chlorides, 

 sulphides and calcium salts. 



Summarising, organic effluents, when dilute, alter the character of the 

 flora and fauna, but at the same time increase the volume. Especially do 

 they cause the growth of the sewage-fungus community and the advent of 

 chironomids and Tubifex. If still stronger, they deprive the water of oxygen, 

 reduce the fauna and increase the volume of sewage fungus. In extreme 

 cases polluted waters have hardly any dissolved oxygen, but show a heavy 

 growth of sewage fungus and a fauna dominated by Chironomus and Tubifex. 

 When an organic effluent ceases partial recovery is rapid, but absolute 

 recovery probably takes some years, especially with water-borne fauna. 



Mr. R. S. A. Beauchamp and Mr. P. Ullyott. — Factors affecting 

 the distribution of Planarias. 



In England the commoner species of stream-living Triclad are Planaria 

 alpina and Poly cells cornuta. Both these animals are stenothermal for cold, 

 and at no stage in its life-history can either resist the effects of drying. 

 Consequently they are only found in streams which have a permanent 

 supply of water. 



In hard water Planaria alpina and Polycelis corfiuta occupy successive 

 stretches of the uppermost reaches of the stream. This zonation, which is 

 controlled by temperature, indicates the presence of calcium, since in soft 

 water it does not occur. 



Of the two species Planaria alpina is the more sensitive to the organic 

 content of the water, so that this species is sometimes absent from streams 

 colonised by Polycelis cornuta. The reason for the absence of Planaria 



