It will be noted that there was increased gain in the closed tubes. Molliard explains the increase here as due to the fact that the assimilation of carbon dioxide was prevented and consequently its injurious action was eliminated. A more probable explanation, in the writer's opinion, is that the plants in the closed tubes had a greater carbon dioxide content available than those in the cotton-plugged tube. As was brought out in the respiration experiments with vetch, a constant elimination of carbon dioxide occurs in the sugar-containing cultures. This carbon dioxide is undoubtedly assimilated, and it is fair to assume that the carbon dioxide produced in respiration in darkness and in the constant respiration of roots affords a supply of greater concentration than that furnished by the normal atmosphere. The writer attempted experiments to test the contention of Molliard, but in each of the several experiments set up complications interfered with the results. In two experiments the plants grown in closed chambers with glucose supplied showed less gain than the plants grown in open chambers with air available. The plants were grown for only twenty days, however, and the experiments were necessarily stopped in each case because of the appearance of molds. Lindet (1911) has stated that fructose induces tissue formation in plants, while glucose is utilized largely in respiration. He found that yeasts, Penicillium glaucum, Aspergillus niger, and the embryos of bean and barley, were influenced similarly by glucose and fructose. Glucose was more readily absorbed than fructose, but contributed largely to respiration. Fructose, on the other hand, in all cases increased the dry weights of the plants much more than did glucose. No cases similar to these have been noted in the writer's experiments, though the superiority of saccharose for vetch and peas may be explained by the work of Lindet. This subject of the rôle of glucose and fructose is now being intensively studied in the Laboratory of Plant Physiology at Cornell. It has been demonstrated conclusively that various sugars can be absorbed by the roots of green plants and that these sugars are assimilated. Not only can sugars be absorbed and assimilated, but investigations show that methyl alcohol, glycerin, certain organic acids, and various organic nitrogenous and other organic substances, may likewise be utilized. The practical significance of these facts is immediately questioned. Does the plant utilize substances from the soil, and, if so, what is their importance in the nutrition of the plant? With respect to the absorption of humus and humate compounds, it has already been stated that J. Laurent (1904) and Mazé (1911) found such absorption. Molliard (1912), on the other hand, as a result of an interesting experiment, came to the conclusion that the humates of the soil are not absorbed. He grew plants under sterile conditions in a closed chamber on a loam rich in humus with no carbon dioxide supplied. The radish showed a slight increase in dry weight, due to the assimilation of carbon dioxide produced from decomposition of the soil humus. From his results Molliard concluded that none of the humus could have been absorbed. The organic content of soils is of course extremely variable and few satisfactory data are available as regards the soluble organic material in the soil. According to Schreiner (1911) the organic content in ordinary soils is large. The average content of 237 types of United States soils, determined by analyses of thousands of samples, is 2.06 per cent for the topsoil and 0.83 per cent for the subsoil. In greenhouse practice the soils used have much higher organic content. In the forcing of cucumbers and tomatoes, for example, this organic content may be as high as 25 per cent or even higher. As stated at the beginning of this paper, the problem of the relation of organic substances to plant nutrition is not merely that of the relation of humus. It is concerned with all the soluble organic substances that must arise from the decomposition of plant and animal residues. The practicability of the power of the plant to utilize to advantage various organic substances rests on the extent to which these substances are found in the soil and the ability of the plant to remove them from weak solutions. There is found in most soils, then, a considerable quantity of organic material, but most of this is in an insoluble state and therefore nonavailable. It is constantly being acted upon, however, by enzymes secreted by microorganisms and by other agents, and soluble organic substances are produced. The soluble organic substances are present in most soils in extremely low concentration, yet their sum total may be as high as or higher 3 During the summer of 1913 a very marked stimulative effect of the fairy-ring fungus Marasmius oreades Fr. was noted on the growth of lawn grass on the Cornell campus, the grass in the region of the ring being darker in color and more vigorous in growth than that in other places. A possible explanation is the digestion of organic material in the soil by enzymes secreted by the fungus mycelium, and the utilization by the grass of the products of digestion. than the dissolved nutrients (Petermann, 1882). Gourley (1915) reports for certain orchard soils in New Hampshire a soluble organic content varying from ninety to two hundred and fifty parts per million. The fact that there exists in soils such a low concentration of soluble organic substances cannot be a serious argument against a direct nutritional value of the soil organic material. The mineral nutrients of the soil and the nitrates are probably present in concentrations no greater; yet these nutrients are constantly being absorbed, and the same is possible for the soluble organic substances, especially those that can be assimilated. The ability of vetch to remove glucose from weak solutions has been demonstrated, and, as stated at the beginning of this paper, the fact that microorganisms and saprophytic plants find in the soil their carbon requirements lends strength to the argument that the higher plants obtain, to their advantage, organic materials from the soil. Schreiner (1911) has called attention to the possibility of the favorable influence on plant growth of nitrogen and phosphorus containing organic compounds of the soil. He states: "The most beneficial manures under normal circumstances are those of organic origin, and the presence of such directly beneficial compounds, like creatinine, in well-rotted stable manure and in green manures, like cowpeas, goes far toward explaining why these manures are more beneficial to soil as a rule than are equivalent parts of fertilizer in the purely mineral forms." It has been demonstrated, however, that not only are organic nitrogenous substances available for plants, but carbohydrates, alcohols, and organic acids and their salts, can also be absorbed by the roots and assimilated by the plants. In view, then, of the established ability of plants to absorb and assimilate organic substances, and in view of the presence in soils of insoluble organic substances which are constantly in a state of transformation to soluble organic compounds, it seems reasonable to conclude, with J. Laurent (1904), that " the organic matter of the soil plays a direct rôle in the nutrition of green plants independently of humus in that the roots are able to find in the soil quantities of directly utilizable organic substances which in a weak measure contribute to the carbon nutrition of the plants." It seems reasonable to conclude, furthermore, that under certain conditions, especially in greenhouse culture, the soil organic material may play a very important rôle in the organic nutrition of plants. 4 Translation from the original French. SUMMARY 1. Corn (Zea mays L.) grown in nutrient solutions containing certain. sugars is able to absorb these sugars by means of their roots, and the sugars are assimilated, effecting increased growth of the plant. 2. The sugars, in the order of their beneficial effect on the plant when grown in the light, are, first glucose and fructose, second saccharose, and third maltose. In the dark glucose again leads, while the other sugars are much alike. 3. The embryo of corn will develop in the absence of all endosperm material, and the presence of maltose increases growth. The production of pigment is progressively increased with the increase in concentration of glucose. 4. Canada field pea (Pisum sativum L.) responds in growth markedly to the presence of sugar; the sugars in the order of their beneficial influence being saccharose, glucose, maltose, and lactose. 5. Timothy utilizes glucose and saccharose, but not lactose when grown in the light. When grown in the dark lactose, as well as the other sugars, appear to be utilized. 6. Experiments with radish (Raphanus sativus L.) confirm the earlier investigations, glucose, saccharose, maltose, and lactose being utilized. 7. Vetch (Vicia villosa Roth) grown in the dark utilizes the various. disaccharides, the order, as regards favorableness, being saccharose, maltose, and lactose. On vetch grown in the light the favorable influence of the different sugars is in the following order: saccharose, glucose, maltose, and lactose. 8. Data are herein presented showing the influence of sugar on the growth and respiration of vetch. The saccharose and glucose cultures are much alike in their effect during the period of the experiment; the maltose culture shows a lesser evolution of carbon dioxide. In the presence of saccharose the seedlings grown in the absence of carbon dioxide maintained practically the original weight of the seed, but in these experiments carbon dioxide equivalent to 0.822 gram of glucose in one case and to 0.8195 gram of glucose in another case was evolved. Somewhat similar results were obtained with glucose and with maltose. 9. The influence of sugar on respiration was manifest as early as the fifth day of the experiment. 10. The carbon dioxide evolution of the sugar-fed plants during the daytime is always appreciably greater than that of the check cultures. This is due in part to a greater root development in the sugar-fed cultures, but also to a greater rate of respiration. 11. Cabbage (Brassica oleracea L.) grown in the presence of maltose shows increased growth. The higher the concentration (2.5 per cent being the highest concentration employed), the greater is the yield of dry matter. A mixture of saccharose and maltose increased growth to a greater extent than 2 per cent of maltose alone. 12. Sweet clover (Melilotus alba Desr.) increases its growth with increased concentration of glucose or saccharose. Crimson clover (Trifolium incarnatum L.) behaves similarly when provided with maltose. 13. Vetch (Vicia villosa Roth) shows increased growth with increase in concentration of sugar. 14. Vetch (Vicia villosa Roth) is shown to absorb glucose from an extremely weak solution. 15. The sugar galactose is toxic to vetch, Canada field pea, corn, and wheat, even at concentrations as low as 0.0125 per cent. 16. The toxicity of 0.05 gram molecular galactose for Canada field pea is antidoted almost entirely by glucose when present at a concentration of 0.10 or 0.20 gram molecular. The toxicity of this solution of galactose is partially antidoted by 0.05 molecular glucose, but practically not at all antidoted when the glucose is less than 0.05 gram molecular. 17. The antagonistic action of glucose toward galactose may be due to its rendering the root impermeable to galactose. It is suggested that the toxicity of galactose may be due to its oxidation products, and that in the presence of glucose the metabolism of galactose may be altered. 18. Evidence was obtained indicating the inversion of saccharose by the roots of vetch, Canada field pea, radish, and sunflower. The inversion was due to invertase probably secreted from the roots. No secretion of maltose or lactose was noted. 19. In the presence of sugar there was noted a marked development of pigment in corn and in vetch. ACKNOWLEDGMENTS The writer is indebted to Dr. J. K. Wilson, of Cornell University, for assistance in some of the early experiments, and to Dr. C. S. Hudson, in |