16 SCIENCE BULLETIN, No. 9. 



This estimate is not, however, supported by experimental figures, and it is 

 to be hoped that Dr. Paterson will be able to continue his investigations so 

 as to include the determination of the transpiration ratio of an average 

 wheat-crop grown in the open under ordinary conditions, since the question 

 is one of the very first importance in wheat-growing in Australia, and in 

 establishing the geographical limits within which wheat-growing can be 

 successfully carried on with us. 



The subject of soil physics is much too wide to come within the scope of 

 an address like the present one, but I have been tempted to draw attention 

 to the possible influence of fertilisers on the movement of soil-moisture, 

 because of the very great importance of the study of moisture conditions to 

 us in Australia. In this connection an interesting investigation has been 

 carried out by Dr. Heber Green and G. A. Ampt* in which are given methods 

 of determining the constants, specific pore space (the free space per unit 

 volume of soil), permeability to water and air, and capillary coefficient. It 

 would be of very great interest to determine the extent to which the 

 addition of fertilisers or soluble salts affect these constants. 



Influence of Fertilisers on Soil-oxidation. 



Another direction in which fertilising substances can function in other 

 Trays than as plant-food is in the promotion of oxidation in soils. 



M. X. Sullivan and Reidf have shown that the oxidising power of soils is 

 increased by the presence of water up to the optimum, and by the common 

 fertilising substances, also by salts of iron, manganese, lime, and magnesia, 

 especially when simple organic hydroxyacids are present. They find that 

 soil-oxidation is comparable with the same process in plants and animals, and 

 that it is greater in surface than in subsoil, arid greater in fertile than in 

 barren soils. 



O. Schreiner and H. S. ReedJ showed that calcium salts, phosphates, and 

 nitrates increase the oxidising power of plant roots, whilst potassium salts 

 tend to retard it. 



Catalytes, or Plant Stimulants. 



There are also a large number of compounds whose presence in minute 

 quantities appear to have very often a quite remarkable effect upon plant 

 growth. These substances cannot be regarded as fertilisers in the ordinary 

 sense. Some of them are of rare occurrence in the soil, or occur only in 

 minute quantities ; many of them are distinctly injurious in any large 

 quantity. We are quite in the dark as to their precise function, and the 

 name " catalytic " has been given to them for want of a better. 



* Journ. Agric. Science, vol. 4, p. 1, and vol. 5, p. 1. 



t Journ. Ind. Evg. Chem., 1911, vol. 3, p. 25. 



Bulletin 56, Bureau of Soils, U.S.A., Dept. of Agric. See also Schreiner, Sullivan, 

 and Reid, Bull. 73, Bureau of Soils, U.S.A., Dept. of Agric. 



A bibliography has been kindly prepared by Mr. L. A. Musso, of the Department of 

 Agriculture, New South Wales, which is printed as an appendix and which may be found 

 useful to those who wish to look up the literature of the subject. An excellent resume 

 of the subject is also published by M. Cercelet, Revue de Viticulture, tome 38, No. 981, 

 p. 381. 



