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BIOLOGICAL STUDIES OF APHIS RUM WIS LINN. 

 REPRODUCTION ON VARIETIES OF VIC I A FABA. 



By J. DAVIDSON, D.Sc. 



{From the Entomological Department, Institute of Plant Pathology, 

 Rothamsted Experimental Station, Harpenden.) 



WITH A STATISTICAL APPENDIX BY 



R. A. FISHER, M.A. 



(With 1 Text-figure.) 



I. INTRODUCTION. 

 The following paper is a continuation of previous work(i) and gives 

 results showing the varying reproductive capacity of Aphis rumicis on 

 eighteen different varieties of field beans. 



My sincere thanks are due to the following gentlemen who very 

 kindly supplied me with seed for these experiments: Prof. J. Percival, 

 M.A., University College, Reading; Mr R. M. Wilson, Principal, East 

 Anglian Institute of Agriculture, Chelmsford ; and The Director, Sveriges, 

 Utsadesforening, Svalof, Sweden. 



My thanks are also due to Mr R. A. Fisher for his kindness and 

 assistance with the statistical considerations involved in this paper. 



The following abbreviations are used in the text : w. v. ? = winged 

 viviparous female; a. v. $ = apterous viviparous female; 1st v. gen. = 

 1st, 2nd, etc. viviparous generations. 



II. METHODS EMPLOYED. 



The plants were grown in unmanured soil to which 10 per cent, of 

 sand was added to prevent "caking" of the surface. Ordinary flower 

 pots, 10 inches in diameter, were used. These were coated on the outside 

 with a layer of wax in order to prevent excessive evaporation. The plants 

 were kept covered with muslin bags throughout the experiments^. 



All the experiments were carried out under similar conditions in a 

 large glasshouse specially designed with large windows and doors. The 



^ The amount of light cut out by these covers was estimated with a thermopile and 

 found to be about 22 per cent. There was very little effect on the growth of the plant. 



