42 



It is possible that the fraction fine silt II., whose upper limit 

 of diameter is .005 mm., has similar effects to the clay fraction. 



XXXII. B. A. Keen. "Evaporation of Water from Soil II. 



Influence of Soil Type and Manurial Treatment." 

 Journal of Agricultural Science, 1921. Vol. XI. 

 pp. 432-440. 

 Further experiments have been done on the evaporation of 

 water from soil, using- the same apparatus and technique as 

 described in an earlier paper. The present series of experiments 

 was desig-ned to investigate the effect of clay content and manurial 

 treatment on the evaporation. Two soils have been used, one 

 containing only 6% clay and the other 15%, and from each soil 

 samples were taken from plots which had received (a) no manure, 

 (h) artificial manure, (c) farmyard manure. The rate at which the 

 soils lost water over concentrated sulphuric acid and at a constant 

 temperature was found to depend firstly on the amount of clay 

 present, and secondly on the amount of organic material in the 

 soil. The differences due to content of organic material were 

 more obvious in the soil containing the larger amount of clay ; the 

 farmyard manure plot lost water at the slowest rate, and the un- 

 manured plot occupied an intermediate position. In the sandy 

 soil the differences in evaporation due to manuring were small. 



There is evidence that the moisture equivalent of these soils 

 measures the percentage of water at which the evaporation is first 

 directly affected by the soil particles, and that at percentages of 

 water in excess of the moisture equivalent evaporation is taking 

 place substantially from a free water surface. 



XXXIII. E. J. Russell and B. A. Keen. ''The Effect of 



Chalk on the Cultivation of Heavy Land." 

 Journal of Ministry of Agriculture, 1922. Vol. 

 XXVIII. pp. 419-422. 

 Measurements taken with a dynamometer showed that dress- 

 ings of chalk applied 8 years ago were still effective in facilitating 

 cultivation, the saving of drawbar pull being in these trials no less 

 than 180 lb. on a three furrow plough (see p. 12). 



THE PLANT IN DISEASE. 



INSECT PESTS AND THEIR CONTROL. 



XXXIV. A. D. Imms. "Recent Research on the Head and 



Month-parts of Diptera.'" Entomologist's 

 Monthly Magazine. 3rd Series, 1920. Vol. VI. 

 pp. 106-109. 

 A short discussion of the subject from the morphological 

 standpoint. 



XXXV. J. Davidson. "Biological Studies of Aphis 



RuMicis Linn. IV. Reproduction on varieties of 

 ViciA Faha — with a Statistical Appendix by R. 

 A. Fisher." (See No. XV.) Annals of Applied 

 Biology, 1922. Vol. IX. pp. 135-145. 

 The reproduction of the bean aphis on 18 \arieties of field 



beans was tested and compared with reproduction on Prolific 



Longpod broad beans. 



