The total soluble carbohydrate fraction of the cotyledons and embryo axis of germinating soybean seedlings declined rapidly during the first 3 days of germination. This depletion began earlier in the embryo axis than in the cotyledon. The total carbohydrate content of the cotyledons of plants grown in light and plants grown in dark was approximately the same for the first 7 days of germination. Between day 9 and 13 the total carbohydrate content of the cotyledons of soybean seedlings grown in dark was higher than that of plants grown in light. The reducing sugar content of light‐grown soybean cotyledons increased approximately 5‐fold during the first 9 days of germination, whereas that of dark‐grown soybean cotyledons increased more slowly during this interval. Reducing sugars in the embryo increased during the early stages of germination until they approximately equalled the total carbohydrate. Between day 4 and 13, oil was depleted more rapidly in the cotyledons of seedlings grown in light than those grown in the dark. The reserve carbohydrates of soybean embryos and cotyledons consisted primarily of low molecular weight oligosaccharides, particularly sucrose, stachyose, and raffinose. These compounds decreased rapidly during germination. The isocitritase activity in the cotyledons of germinating soybean seeds increased rapidly for the first 6 days of germination and then decreased for the next 7 days. The isocitritase activity of plants grown in the dark was higher than that of the plants grown in light at all stages of development, particularly between day 7 and 11.

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During the initial phase of germination and seedling development of soybeans, most of the increase in dry weight in the embryo axis occurred in the hypocotyl. The epicotyl did not undergo a rapid increase in size and dry weight until the 4th to 5th day of growth. From day 1 to 11 dry weights of the hypocotyls in the “CO2‐normal” and “CO2‐Iimiting” (less than 50 ppm [0.005%] atmospheric CO2) treatments were similar. By day 13 the CO2‐normal hypocotyls had continued their rapid increase in dry weight while the dry weight of the hypocotyls grown under CO2‐limiting conditions had decreased. The parallel decrease in dry weight of the cotyledons that occurred for both CO2 treatments (days 1 to 13) suggested that CO2 content of the atmosphere is not a controlling factor in the digestion or hydrolysis of food reserves in the cotyledon during germination and seedling development. This is supported by the failure of the CO2 treatments to produce significantly different patterns in utilization of lipids, total carbohydrates, or proteins in the cotyledons. The seedlings grown under either the limiting or normal CO2 atmospheres utilized their cotyledonary carbohydrates and lipids before the proteins. Sufficient food reserves are present in the soybean cotyledon storage cells for seedling development until about day 9. Net CO2 uptake by soybeans in a CO2‐normal environment first occurred between days 9 to 11.