Seasonal Variations in the Carbohydrates in the Xylem of Antiaris africana

The xylem of Antiaris africana contains sucrose, starch, glucose,fructose, maltose, and raffinose. Sucrose and starch are themost abundant carbohydrates. Glucose and fructose occur in relativelyequal amounts while maltose and raffinose are the least abundant.Raffinose disappears from the xylem during the dry season, justbefore leaf fall. The pattern of seasonal variation in the individualsugars and starch is similar. There is generally a peak at leaffall and a depletion of these reserves at new flush. Accumulationof carbohydrates during leaf fall occurs first in the youngestxylem (i.e. the 0–2-cm segment). The youngest xylem alsoaccumulates the greatest amount of reserve sugars and starch.The concentrations of the sugars decrease inwards until theybegin to rise after the 4–6-cm segment. There is, however,no such rise in the concentration of starch. The dry-mattercontents increase inwards from the youngest xylem until theylevel out after the 4–6-cm segment. There is a rapid fallin the sucrose and starch contents of felled A. africana. Sucrosedropped by about 65 per cent and starch by about 73 per centin the first 10 days after felling. The levels of other sugarsdecreased gradually except for glucose and fructose which initiallyrose and then fell. Glucose and maltose could still be detectedon the 68th day after felling.