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Carbohydrates in Grasses. II. Sugar and Fructosan Composition of the Stem Bases of Bromegrass and Timothy at Several Growth Stages and in Different Plant Parts at Anthesis¹

The predominant fructosans in timothy varied in molecular weight with growth stage and plant part. At mature growth stages when the water-soluble carbohydrate content was high, a series of fructosans was present in the stem bases and they were predominately of longchain length. Only short-chain fructosans were found in the stem bases during periods of active vegetative growth when water-soluble carbohydrates were low. Timothy plants at anthesis contained only short-chain fructosans in the inflorescence, leaf blades, and in the upper sheaths and internodes, but the lower sheath, internodes, and roots contained predominately long-chain units. Fructosans were of short-chain length in all comparable samples of bromegrass. The chain lengths of fructosans were relative determinations based on their differential solubility in various elhanol concentrations and water.

The percentages of total free sugars, fructosans, and total water-soluble carbohydrates in bromegrass at anthesis increased from the top to bottom leaf blade, sheath, and internode above the stem base. Such a gradient was noted only among the internodes of timothy for the later two fractions.

At anthesis, the stem (internodes plus the stem base) of both species contributed the largest proportion of the grams of total dry matter and total water-soluble carbohydrates in the tillers, followed by the inflorescence. The contributions of the leaf blades atid sheaths were least and similar.

² Professor of Agronomy, Wisconsin Agr. Exp. Sta. The author acknowledges the help of Research Assistants R. D. Grotelueschen, C. J. Nelson, and D. P. Knievel in conducting the chemical analyses.

Received for publication August 18, 1966.