CARBOHYDRATES 151 



of polysaccharide character (or related to polysaccharides) are known, 

 and these may be obtained from leaves, stems, roots, and even flowers, 

 beyond a few generalizations (for example, their association with the 

 Leguminosae and specific genera therein such as Acacia and Astra- 

 galus), very little systematic importance is indicated for them at the 

 present time. It is still considered likely that certain gums are 

 synthesized by fungal or bacterial enzymes rather than via a metab- 

 olism strictly that of the host. This point is discussed briefly in the 

 comprehensive treatment of plant gums and mucilages by Smith and 

 Montgomery (1959). 



Araban is composed of L-arabinose units. It is a common 

 constituent of pectic materials and is very widely distributed. Xylans, 

 whose chief constituent is xylose, occur in several forms, frequently of 

 1 : 4 y8-linked D-xylopyranose units in unbranched or branched chains. 

 It is highly probable that the specific xylans would prove to be sys- 

 tematically valuable, but as yet there is inadequate knowledge from 

 an insufficient number of species. 



Galactans, which also comprise part of the pectin complex are 

 quite common. Arabogalactans are associated with the woods of 

 conifers, particularly various species of larch (for example, Larix 

 occidentalis). Mannans are widely distributed among higher and 

 lower organisms. Galactomannans are also known from a number of 

 species, and according to Neumuller (1958), they are associated 

 particularly with the family Leguminosae (for example, Medicago 

 sativa produces a galactomannan with a ratio of galactose to mannose 

 of 2 : 1). Glucomannans are known from several species of Amorpho- 

 phallus (Araceae) and seeds of certain Iris species. 



Polyglucosides other than starch include such substances as 

 floridean starch and laminarin. The former is formed as the reserve 

 carbohydrate in red algae; the latter as the reserve carbohydrate in 

 brown algae. Floridean starch has recently been studied in detail by 

 Meeuse et al. (1960), who conclude that there is no basic distinction 

 between this starch and other polysaccharides of the starch family. 

 Floridean starch appears to have a branching pattern similar to that 

 of glycogen, that is with somewhat more frequent, shorter 1 : 6 side 

 chains than the amylopectin component of typical starch. 



Algae also produce several other unusual types of polysac- 

 charides, some of which are httle known chemically. Recently, Stoloff 

 and Silva (1957) attempted to apply the distribution of particular 

 water-soluble polysaccharides to the phylogenetic treatment of sixty 

 species of red algae. The classification of the polysaccharides is based 

 mostly on physical properties. Three types, all of which occur esteri- 

 fied with sulfate residues attached to galactose units, were described: 



