RELATION OF FERTILISERS TO SOIL FERTILITY. 17 



H. Ost found small quantities of fluorine to be always present in a number 

 of healthy leaves which he examined. 



Aso, Oscar Loew, Ampola, and others, show that small quantities of 

 fluorine have a stimulating effect on many plants. Iodine has been shown 

 also to stimulate the growth of plants when in small quantities. Oscar 

 Loew and the Japanese chemists, who have done a great deal of work in 

 experimenting with the foregoing elements, and with lithium, caesium, and 

 uranium, find that they stimulate the growth of a number of plants both in 

 the field and in pots. Titanium has also been found to increase the yield of 

 crops. C. E. Wait has found titanium in the ash of every plant which he 

 has examined, and Annett states that the colour of the black cotton soil of 

 India is due to the presence of a titaniferous mineral. I have found 

 titanium to be present in soils of the black-soil plains in the north-west of 

 New South Wales, but cannot assert that this is the cause of their colour, 

 since other soils, from the same locality and derived from the same minerals, 

 which are red or chocolate in colour, also contain titanium. The addition of 

 flowers of sulphur has also been found to improve the yield of many crops. 

 {Copper is stated by some writers to increase plant growth when present in 

 small quantities, but by others to be injurious. Boron appears to be very 

 widely distributed in the plant world, and the proof of its presence as a 

 natural constituent of grapes and of wines is of considerable economic 

 interest. At the rate of ^ gramme per square metre it has been found 

 by Agulhan to increase enormously the yield of wheat, maize, rape, and 

 turnips. 



The literature with regard to manganese, its occurrence in plants, and the 

 action of minute quantities, is voluminous. In minute quantities it appears 

 to be beneficial, in larger quantities toxic, and its toxicity appears to increase 

 with its stage of oxidation. 



Other substances that may be mentioned in this connection are vanadium, 

 chromium, nickel, barium, zinc, mercury, didymium, and glucinum. 



For the most part these substances are plant poisons, but quite remarkable 

 benefits have been obtained by their application in very small quantities. 



It may very well be that some extremely important discovery may be 

 made as the result of the study of these catalytic fertilisers, one that may 

 throw some light on the question of plant assimilation. Among the most 

 striking results obtained to date appears to be the very remarkable effects 

 produced by some of these metallic salts upon moulds the effect, for example, 

 of zinc upon the development of Aspergillus niger, ten times the quantity of 

 this mould being produced in solutions containing 1 in 50,000 of zinc. 



The subject of catalytic fertilisers, or the action of small quantities of 

 substances on plant growth, is an extremely fascinating one, but too little is 

 known of the mechanism of the processes involved to make it desirable to 

 pursue the subject further in this place. It affords additional illustration of 

 the fact that the beneficial action of so-called fertilising substances is not 

 con tined to supplying the plant with food. 



