1. The cell wall of Fusicoccum amygdali consisted of polysaccharides (85%), protein (4-6%), lipid (5%) and phosphorus (0.1%). 2. The main carbohydrate constituent was d-glucose; smaller amounts of d-glucosamine, d-galactose, d-mannose, l-rhamnose, xylose and arabinose were also identified, and 16 common amino acids were detected. 3. Chitin, which accounted for most of the cell-wall glucosamine, was isolated in an undegraded form by an enzymic method. Chitosan was not detected, but traces of glucosamine were found in alkali-soluble and water-soluble fractions. 4. Cell walls were stained dark blue by iodine and were attacked by alpha-amylase, with liberation of glucose, maltose and maltotriose, indicating the existence of chains of alpha-(1-->4)-linked glucopyranose residues. 5. Glucose and gentiobiose were liberated from cell walls by the action of an exo-beta-(1-->3)-glucanase, giving evidence for both beta-(1-->3)- and beta-(1-->6)-glucopyranose linkages. 6. Incubation of cell walls with Helix pomatia digestive enzymes released glucose, N-acetyl-d-glucosamine and a non-diffusible fraction, containing most of the cell-wall galactose, mannose and rhamnose. Part of this fraction was released by incubating cell walls with Pronase; acid hydrolysis yielded galactose 6-phosphate and small amounts of mannose 6-phosphate and glucose 6-phosphate as well as other materials. Extracellular polysaccharides of a similar nature were isolated and may be formed by the action of lytic enzymes on the cell wall. 7. About 30% of the cell wall was resistant to the action of the H. pomatia digestive enzymes; the resistant fraction was shown to be a predominantly alpha-(1-->3)-glucan. 8. Fractionation of the cell-wall complex with 1m-sodium hydroxide gave three principal glucan fractions: fraction BB had [alpha](D) +236 degrees (in 1m-sodium hydroxide) and showed two components on sedimentation analysis; fraction AA(2) had [alpha](D) -71 degrees (in 1m-sodium hydroxide) and contained predominantly beta-linkages; fraction AA(1) had [alpha](D) +40 degrees (in 1m-sodium hydroxide) and may contain both alpha- and beta-linkages.

1. The nature of two polysaccharides (s(0) (20) values 6S and 2S respectively in 1m-sodium hydroxide), comprising a fragment (fraction BB, [alpha](D) +236 degrees in 1m-sodium hydroxide), previously isolated from cell walls of Fusicoccum amygdali, has been investigated. 2. Both the major (2S) and minor (6S) components were affected by incubation with alpha-amylase. The 6S polysaccharide was also attacked by exo-beta-(1-->3)-glucanase, which is evidence that it contained both alpha-(1-->4)- and beta-(1-->3)-glucopyranose linkages. By fractionation of the products of alpha-amylase-treated fraction BB it was possible to obtain a water-insoluble polysaccharide, fraction P ([alpha](D) +290 degrees in 1m-sodium hydroxide, 67% of fraction BB) and a water-soluble polysaccharide, fraction Q ([alpha](D) +16 degrees in 1m-sodium hydroxide, 11% of fraction BB), both of which sedimented as single boundaries with s(0) (20) values (in 1m-sodium hydroxide) of 1.7S and 4.6S respectively. 3. Evidence from periodate oxidation, methylation analysis, i.r. spectroscopy and partial acid hydrolysis showed that fraction P consisted of linear chains of alpha-(1-->3)-glucopyranose units with blocks of one or two alpha-(1-->4)-glucopyranose units interspersed at intervals along the main chain. The 2S polysaccharide, from which fraction P is derived, evidently also contains longer blocks of alpha-(1-->4)-glucopyranose units, that are susceptible to alpha-amylase action. 4. Fraction Q consisted of glucose (88%) with small amounts of galactose, mannose and rhamnose. Evidence from digestion with exo- and endo-beta-(1-->3)-glucanases, periodate oxidation and methylation analysis suggests that fraction Q consists of a branched galactomannorhamnan core, to which is attached a beta-(1-->3)-, beta-(1-->6)-glucan. In the cell wall, chains of alpha-(1-->4)-linked glucopyranose units are linked to fraction Q to form the 6S component of fraction BB.