Mineral and organic nutrients in sieve tube exudate and xylem vessel sap of Quercus rubra L

On October 10, 1974, sieve tube exudate samples were collected from a small number of 16-20 years old Quercus rubra trees growing in the woods near Lunteren. The method of collection was the one described by Hartig (1858) and applied by Munch (1930). Small cuts were made in the bark at a height of about 1.7 m and exuding drops were picked up with hard-glass capillaries. On October 27, when about half of the leaves had dropped, two of the trees were almost completely cut off at a height of 1.8 m. The tree parts above the cuts came down and their branches were chopped away, leaving stem parts of about 4 m length partly connected with the bottom parts of the stems but making an angle with them in a downward direction. From the lowest wound surface a water-like fluid flowed out the wood with a rate of about 25 ml in 20 min. The first ml were disregarded as they contained some saw dust and other contaminants of the cut surface. The fluid collected in this way is considered to represent the xylem vessel contents, which due to the very wet autumn, the early dropping of the leaves and the probably still active root system was apparently abundantly present in the wide xylem vessels. One week later, under similar weather conditions, only 2 ml could be collected from one of the two trees cut down for this purpose.