Seedlings of seed varying in their proportions of carbohydrates to N were grown on their own N reserves to maximum size in light and in darkness. Similar lots of seedlings were given extra N as nitrates. In corresponding tests seedlings were grown in the light and on their own C reserves and with and without nitrates; with extra C in the form of CO2 (0.4%); and with and without nitrates. The seedlings were grown in sterilized quartz sand moistened with nutrient solutions. (1) Total growth Seedlings of low-protein seed are unable to make use of 0.4% CO2 except for slight increases in growth of roots noted in some cases (low-protein wheat); shoots of such seedlings are even retarded by the extra CO2. Only when nitrates are added does the CO2 become beneficial. Light causes increased total growth (green weight) of seedlings of low-protein seed only if nitrates are available. (2) Modifications in shoot to root ratios: When N becomes limiting, it restricts the growth of shoots more than of roots and extra N as nitrates increases the growth of shoots more than of roots. When C becomes limiting, it restricts the growth of roots more than of shoots, and added C as CO2 increases the growth of roots more than of shoots. The growth responses of seedlings to varying proportions of carbohydrates to N agree with results obtained with tomato cuttings, described in former papers. The indications are that early application of nitrates would not be beneficial to all types of plants, but field tests will be required definitely to answer the question.