Hourly Variations in Carbohydrate Content of Leaves and Petioles

Data on carbohydrate metabolism are presented which were gathered from the potato, soy bean, and sunflower during the summers of 1926 and 1927. 2. Distinct differences in rapidity of formation and translocation of carbohydrates were observed in plants grown under the favorable environmental conditions of 1926 and the unfavorable conditions of 1927. 3. Sucrose apparently is not the first sugar formed by leaves, nor is it formed as a by-product of vacuolating protoplasm. Its function in the leaf seems to be that of temporary storage. 4. The simple sugars (hexoses and pentoses) seem to be the first sugars synthesized by plants. 5. From the data, observations are made which impose certain requirements upon any theory which attempts to explain the translocation of food materials from the leaves. 6. Variations in the content of hemicelluloses are not only large but frequent in leaves growing in a favorable environment. Under such conditions these materials apparently serve as temporary reserves. 7. When growing conditions are unfavorable, due to deficient moisture or warmth, the amount of hemicelluloses is relatively large but fluctuations are not observed. 8. A plant which is capable of producing and maintaining a large content of hemicelluloses in its leaves apparently can resist drought.