364 SECTIONAL TRANSACTIONS.— D. 



much the same manner as untreated sewage. The lubricating oil has a 

 bad effect upon smaller stream organisms such as insects. The dust tends 

 to smother the water-weeds. 



There is no doubt that washings from roads surfaced with ordinary 

 tar contain such definitely poisonous substances as phenol, cresols, naph- 

 thalene and quinoline. 



As England is a great producer of tar, this toxicity is unfortunate because 

 road-engineers, to save themselves from the execrations of anglers, have 

 used large quantities of non-toxic bitumen which is imported from abroad. 



The tar industry, however, faced with this heavy loss, have not been 

 idle, and have carried out much intensive research. Tars which are vir- 

 tually non-toxic are now commercially available. Apart from their low 

 toxicity, these tars have valuable physical properties which make them a 

 formidable rival of bitumen. 



Cement, when first laid, is dangerous because of its content of free lime 

 but, when matured, it contains no substances which are poisonous to stream 

 life. 



Mr. F. T. K. Pentelow. — The growth of trout in acid zoaters (2.45). 



Brown trout {Salmo trutta) vary greatly in their adult size. In general, 

 in this country, fish living in alkaline, calcareous waters grow big (2 to 5 lb.) 

 whilst those in neutral or acid waters never exceed a few inches in length or 

 a few ounces in weight. In Sutherland there are certain lochs containing 

 very soft, acid waters (pH 4-5) in which trout grow to 4 or 5 lb., whilst 

 there are other neutral lochs {pH 6 -5) in which the fish are small. 



The geology, chemistry, flora and bottom fauna of these two types are 

 briefly described and various theories of trout growth re-examined in the 

 light of these data. 



Mr. K. A. Pyefinch. — Wollaton Park Lake, Nottingham : a physico- 

 chemical survey (3.0). 



This is a brief account of the more important physico-chemical changes 

 taking place in a small, shallow lake, based on a two years' survey. 



Such temperature gradients as occur are purely transient, as they are 

 abolished during the night or by a short period of unfavourable weather 

 during the day. The annual changes of pH and oxygen are conditioned 

 by the extent and by the type of flora ; there is no midsummer stagnation 

 period. Diurnal changes in oxygen content are often well marked. 



The annual changes in phosphate, silicate and nitrate are generally 

 normal, though there are anomalies in the phosphate readings. The 

 abnormal summer rainfall of 1936 led to the inflow of water rich in phosphate 

 and silicate, though the nitrate values were not much affected. 



It is not possible to draw any definite conclusions as to the factors which 

 may limit the development of the flora. Lack of phosphate has been 

 generally quoted, but these investigations show that the limiting factor 

 may vary from year to year and that observations made in the lake alone 

 may be deceptive, as an inflow of water comparatively rich in the essential 

 solutes may be going on all through the summer. 



Mr. C. R. Sto'SOR.— Some features of the courtship display of the Birds of 

 Paradise (3.30). 



Field observations and study of the birds in captivity shows that the 

 remarkable displays of the Birds of Paradise are sexual in nature and are 



