SECTIONAL TRANSACTIONS.— M. 521 



of the economic characteristics of plants in genie terms and the solution of 

 such problems as hybrid vigour ; and as self-sterility and cross-compatibility, 

 with their implications in productivity. 



Farmers have an important part to play in a greater discrimination of 

 varietal merit and a firmer insistence upon proofs of it. General policy in 

 plant breeding must inevitably be of very long range and its nature and 

 soundness are completely dominated by the national policy adopted by the 

 country for its agriculture as a whole. 



Mr. C. T. GiMiNGHAM. — Crop pests and diseases (ii.o). 



The fact that insect pests and fungus diseases are important factors in 

 crop production is generally accepted, but the continuous toll taken by them, 

 and the extent of the losses sustained, are perhaps less commonly realised. 

 In recent years, practical and economic means of dealing with several 

 important pests and diseases, previously very difficult to control, have been 

 found, but, on the other hand, there are many unsolved or only partially 

 solved problems requiring investigation. Some examples are given. 

 Control measures need to be considered strictly in relation to the value of 

 the crop, and the problems are thus often most difficult where the less 

 valuable agricultural crops are concerned. Some of the factors affecting 

 the natural limitation and artificial control of plant pests and diseases are 

 shortly discussed, particularly in relation to cultural conditions. 



General Discussion opened by Sir John Russell, F.R.S. (11.30). 



Afternoon. 

 Visit to farms of Messrs. Chivers & Sons, Ltd., Histon. 



Tuesday, August 23. 



Discussion on The practical problems of animal production (lo.o). 



Prof. R. Rae. — Animal husbandry. 



Prof. F. A. E. Crv.v/.— Animal breeding (10.30). 



Dr. E. L. Taylor. — Parasitic diseases of animals (ii.o). 



Parasitic worms are responsible for the most economically important 

 diseases of grazing animals throughout the world. There is little doubt, 

 however, that in the original primitive state they were relatively harmless, 

 forming part of a well-balanced ecological unit in which the parasites and 

 parasitised animals lived harmoniously together. To a very considerable 

 extent the diseases which parasitic worms now cause are man made, having 

 been brought about by the enclosure of grazing land and the improvement 

 of pasture. The particular types of parasitic worm which are of the greatest 

 concern are ubiquitous in their distribution, a light infestation being regarded 

 as normal and causing no disturbance of health. A heavy infestation is, 

 however, harmful, and as the number of parasites tends to increase with the 

 square of the concentration of grazing animals the effect of the unnatural 

 crowding of the animals increases progressively as pasture land is improved 

 and severe losses from worm disease frequently occur. 



The successful development of the individual worms depends, however. 



