539 
Food Substances for Plant Groivth . 
traces of the growth substances absorbed by the embryo before the seed was 
cut off. The plants with the silver fraction, however, show a progressive 
increase in weight, which was manifest by an increase in size whilst the 
experiment lasted. The result appears to support the view that during 
germination certain substances are developed which enable the embryo to 
utilize the food material present in the seed, and that these substances can 
be replaced in whole or part by the silver fraction from an extract of 
bacterized peat. 
One striking fact connected with these substances is that they are 
active in extremely minute quantities, 0-35 part of the silver fraction per 
million parts of culture solution being sufficient to give the results quoted 
above. 
The chief interest of these experiments centres round the possibility 
that the nutrition of a plant depends, not only upon the supply of mineral 
food constituents, but also upon a supply of certain accessory organic food 
substances, very small amounts of which are sufficient to supply the needs 
of the plant. During the early stages of growth of the embryo, these 
substances are supplied by the seed ; later when the young plant is able to 
maintain itself, they are obtained from the humus of the soil. 
How far this theory is a correct one can only be decided by further 
careful experiments which are now in progress. In view, however, of the 
growth results obtained by ordinary water-culture methods in the labora- 
tory it must be noted that the above results were only obtained by using 
chemically pure salts and physiologically pure distilled water, thus avoiding 
any possible inclusion of traces of soluble organic matter. Care was also 
taken to prevent any bacterial or algal contamination ol the culture 
solutions. 
Nothing definite can yet be stated as to the nature or composition 
of these growth-stimulating substances, but experiments in progress appear 
to indicate that they resemble more closely the accessory food factors of 
Hopkins than the vitamines of Funk. 
In conclusion, I wish to express my indebtedness to Miss Mockeridge, 
B.Sc., for her valuable assistance with the chemical part of this investigation ; 
also to thank Mr. Watson of the Royal Gardens, Kew, and Mr. Hales of 
the Chelsea Physic Garden, for their kindness in carrying out a series of pot 
experiments. 
