In the summer of 1912 the author well remembers how he and others were impressed with a remarkable lecture delivered by Professor Gabriel Bertrand, of the Sorbonne, Paris, on the effect upon the growth of plants of minute additions of one or two elements, particularly manganese. One part of manganese in one million of the culture solution appreciably increased the growth of molds. It was inevitable that such profound influences due to microscopic amounts of substances should give rise to much speculation. Scientists recalled such substances as adrenalin and iodine which are present in minute amounts in glands of the body, and which exert a profound influence upon our well-being. And above all, there are these enzymes, which forever synthesize and analyze materials in the plant and animal kingdom, and which also are present in such minute quantities.

Next came an unfolding of the entire field of vitamines, an account of which we have already given. Here again the effective quantities are ridiculously small. These little things that are brought with such difficulty within our sphere of vision are equally important with the bigger things that our senses grasp much more easily.

Do Plants Need Vitamines? If animals need vitamines, do plants? And if so, where do the plants get them? We have already seen that our vegetable products may contain vitamine (see also the summary), but to what extent, if any, do they themselves need them? Or do the plants merely build these vitamines so as to supply us with a necessity?

Auximones

We owe whatever information we have on this subject to Professor Bottomley, an English botanist. He has shown that the prevalent idea that the plants merely need simple inorganic materials, such as carbon dioxide, water, and mineral salts in order to build up their organic structure, is erroneous. Working with several varieties of green plants, Professor Bottomley has been able to prove that "the addition to the inorganic nutrients of minimal quantities of certain organic substances is absolutely essential if the plants are to grow healthily and normally for any length of time." What was added was not really a pure organic substance, but a complex mixture; but the mixture contained an unidentified substance which had the power of maintaining life and stimulating growth in plants. This unidentified substance - or substances? - Professor Bottom-ley calls an auximone.

Auximones and Vitamines Are Probably Identical. Now the reader will need to use little of his imagination to see how readily this idea of auximone in plants fits in with the vitamine hypothesis in animals. Professor Bottomley himself was the first to recognize that his auximones are similar in function to the vitamines, though not necessarily so in nature.

Where do these auximones, or vitamines, or growth-promoting substances in plants come from? They are organic in nature - presumably; that leads to the supposition that they are derived from the organic matter of the soil in which the plant is growing.

"Organic matter of the soil" is still rather vague. The soil is very complex and much of it is organic - a complex mixture of carbon compounds plus no end of bacteria. Here again Professor Bottom-ley, and Miss Mockeridge, his assistant, bring us enlightenment; for they have noticed that whenever peat is attacked by soil bacteria so that it decays, plant vitamines appear in much force. Such a decomposing peat can be shaken with water, and the watery extract can then be shown to stimulate plant growth and also to stimulate soil bacteria particularly the type that bring about the decomposition of peat. This has led to the suggestion that the plant vitamines - and in the ultimate analysis this would include the animal vitamines - are actually produced by soil organisms. In support of this contention Professor Bottomley has performed experiments which illustrate how, whenever the bacterial activity in the soil increases, we get a corresponding increase in vitamine activity. The organic manures usually applied in agriculture, such as leaf mold and stable manure, were examined. They all contained varying proportions of water-soluble vitamine corresponding to the water-soluble B variety with which we are already familiar. But in every instance an extract of well-rotted manure, where bacteria are particularly abundant, was far more effective in bringing about growth in plants than an extract of fresh manure. Just as with the vitamines the animal needs, the amount of plant vitamine that the plant needs is so small, that such an addition to the plant nutrients cannot materially add to their calorific value.*

* Mr. C. H. Richardson, of the Government Bureau in Washington, is engaged in experiments with insects which tend to show that vitamines are just as important to them as they are to us and to plants (private communication from the author); and we have good reasons for believing that yeasts and bacteria need these vitamines too.