Growth of Lemna minor in Mineral Culture Solutions. 505 



Seidell* to indicate, with certain reservations, the presence of animal 

 growth vitamines. 



It is possible that both organic plant nutrients and accessory food 

 substances were present in the complex water extract of bacterised peat 

 supplied in the above experiments, and that these had a co-operative effect, 

 for, even if one assumes that the phosphotungstic fraction contained only 

 accessory food substances, it is seen that the more complex water extract 

 produces the best growth results. 



In view of the generally accepted botanical theory that green plants can 

 build up complex protein compounds from mineral salts, and mineral salts 

 only, the above results are difficult to explain. If this theory be correct, 

 then Lemna minor must either have lost this power, or it is an exception 

 to the general rule, since it is evident that, for healthy growth, this plant 

 must be supplied with small quantities of certain organic substances in 

 addition to mineral nutrients. The beneficial effect of organic manures in 

 cultural operations is well known. Eecently Livingstonf has shown that 

 manure extract and the expressed juice of red-clover leaves have a remarkable 

 effect in increasing the growth of wheat seedlings in culture solutions con- 

 sisting of soil extracts and mineral nutrients. He demonstrates that it is 

 the organic matter of the extracts which is beneficial, but he attributes the 

 benefit to " some correcting influence which it brought to bear upon the 

 toxic bodies of the soil extract and those which appear to be produced by 

 the seedlings " rather than to a direct action upon the nutrition of the 

 plants. 



The remarkable effect of the addition of organic substances in the experi- 

 ments on Lemna minor recorded above, as manifested not only by the 

 enormous increase in number and weight of the plants, but also by the 

 increased vigour of the individual cells, as shown by the denser protoplasm, 

 larger nuclei and more numerous chloroplastids, indicates that the organic 

 substances play some definite and essential part in the general metabolic 

 activities of the plant. 



To what extent certain organic substances may be necessary for the 

 growth of green plants in general, further experiments alone can decide. 

 The well-known fact that the seedlings of land plants can be grown to 

 maturity in culture solutions of mineral salts is not a fatal objection to the 

 suggestion that all green plants may require traces of certain organic 

 substances for their optimum development, since it has been shown that 

 nitrogenous organic growth-promoting substances are produced during the 



* Williams and Seidell, ' Jour. Biol. Chem., 1 vol. 26, pp. 431-456 (1916). 

 t Livingston, B. E., U.S. Dept. Agric, Bureau of Soils, Bull. 36, 1907. 



