PROCEEDINGS OF SECTION K. 659 



The subject of catalytic fertilizers, or the action of small quan- 

 tities of substances on plant growth, is an extremely fascinating 

 one, but too little is known of the mechanism of the processes in- 

 volved to make it desirable to pursue the subject further in this 

 place. It affords additional illustration of the fact that the bene- 

 ficial action of so-called fertilizing substances is not confined to 

 supplying the plant with food. 



The minute quantities used are quite inadequate to supply 

 plant food in the generally accepted sense of the term. For ex- 

 ample, Aso, in some experiments with peas (see bibliography 

 referred to above) found that the growth of the crop was stimulated 

 and the yield increased by 0.001 gramme sodium fluoride per 2 to 

 3 kilos of soil. 



Another Japanese investigator (see bibliography) found 940 

 grammes of the same salt per hectare to benefit barley and certain 

 grasses. 



In the cases also where these substances act as plant-poisons the 

 proportions are exceedingly minute. Similarly we know that iron- 

 salts are necessary for the production of chlorophyll, and that, in 

 the absence of iron in the soil, or culture medium, the chloro- 

 phyll cells do not develop, and yet chlorophyll itself contains no 

 iron. 



There is some action of which we are ignorant in all these cases, 

 for an explanation of which we must wait for the plant physio- 

 logist. 



Recent work by Willstatter, Marchlewski, and others has estab- 

 lished the fact that a great similarity exists between some of the 

 products of the green colouring matter of plants and the haemo- 

 globin or red-colouring matter of the blood of animals and human 

 beings. It has been shown that chlorophyll is a magnesium com- 

 pound, and contains no iron, which latter is an essential constituent 

 of the red-colouring matter of the blood. It would appear as if 

 the peculiar property of chlorophyll to absorb and split up carbonic 

 acid is due to the presence of magnesium in the chlorophyll mole- 

 cule, whereas its replacement by iron effects the absorption of 

 oxygen. We know of similar instances in which the introduction 

 into an organic molecule of metallic or elementary atoms results 

 in remarkable physiological activity. Ehrlich's celebrated specific 

 against syphilis (a definite amido-benzol compound containing 

 arsenic) is one of the best known instances in point. Wassermann 

 has used a selenium derivative of eosin successfully in the cure of 

 cancer in mice. 



A number of similar compounds are at present under trial, par- 

 ticularly in the case of cancer. 



The remarkable effects produced by the entrance of such elemen- 

 tary atoms into the molecule is a fact of the highest significance, 

 not only in the study of disease in men and animals, but in plant 

 physiology. 



