The molecular structure and chemical properties of the hemicellulose present in the isolated cell walls of suspension cultures of sycamore (Acer pseudoplatanus) cells has recently been described by Bauer et al. . The hemicellulose of the sycamore primary cell wall is a xyloglucan. This polvmer functions as an important cross-link in the structure of the cell wall; the xyloglucan is hydrogenbonded to cellulose and covalently attached to the pectic polymers.The present paper describes the structure of a xyloglucan present in the walls and in the extracellular medium of suspension-cultured Red Kidney bean (Phaseolus vulgaris) cells and compares the structure of the bean xyloglucan with the structure of the sycamore xyloglucan. Although some minor differences were found, the basic structure of the xyloglucans in the cell walls of these distantly related species is the same. The structure is based on a repeating heptasaccharide unit which consists of four residues of 13-1 ,4-linked glucose and three residues of terminal xylose linked to the 6 position of three of the glucos;yl residues.A structural model of the primary cell wall of suspensioncultured sycamore (Acer pseudoplatanus) cells has recently been obtained (3,9,15). Xyloglucan, which accounts for 21% of the cell wall, is one of the seven major structural polymers of this wall. The xyloglucan has been operationally defined as a hemicellulose because it has the ability to hydrogen-bond strongly to cellulose (2,3). In the sycamore cell wall, xyloglucan is hydrogen-bonded to cellulose and is covalently attached, through its reducing end, to the pectic polymers of the wall (3, 9). Since xyloglucan functions as an important cross-link in the wall, we have examined the distantly related angiosperm, Red Kidney bean (Phaseolus vulgaris), to find whether its cell walls possess a similar hemicellulose and, if so, to determine which structural features of this polymer have been conserved or altered during evolution. 'To whom reprint requests should be addressed. MATERIALS AND METHODS