Nutrition Investigations. 273 



particular organ or tissue, being found abundantly in roots, stems, 

 leaves or seeds. 



In regard to solubility in water, pentosans show all possible varia- 

 tions. De Chalmot (108) found them present in the watery extract of 

 the leaves of many plants; Winterstein (167) in the somewhat mucila- 

 ginous hot water extract of the seeds of Tropaeolummajus ; Schulze (146), 

 in both soluble and insoluble form in the cotyledons and endosperms 

 of the seeds of Lnpinus luteus and other legumes, where they are doubt- 

 less stored as reserve material for the growing plant; and in the cell 

 walls of the mature plants, where in most cases they approach true cel- 

 lulose in character. It is difficult to differentiate these highly resis- 

 tant pentosans of the cell wall, which are commonly included in the 

 term crude fiber, from the ligno-celluloses and oxycelluloses also 

 found there, which as Cross, Bevan and Beadle (104) have shown,* 

 are like true pentosans in yielding furfurol on distillation with dilute 

 hydrochloric acid. Besides hemicelluloses yielding pentoses {xylose 

 and arabinose) exclusively, occur many yielding also methyl-pentoses 

 (fucose, rhamnose) . These yield on distillation with dilute hydrochloric 

 acid, methyl-furfurol, which is precipitated by phloroglucin, and hence 

 included in quantitative estimations of pentosans by the method of 

 Tollens andKrober (121). The distribution of methyl-pentosans has 

 been studied especially by Tollens and his pupils. Japanese "Nori" 

 {Porphyra laciniata, Laminar ia, and other seaweeds) (129), tragacanth 

 and many other gums (163) contain fucosan. Rhamnose occurs also 

 widely distributed in the plant kingdom, but more frequently in the 

 form of a glucoside. Rohmann (134) reports a rhamnosan in Ulva 

 lactuca. 



It is a very common thing to find pentosans and hexosans occurring 

 together. In fact, it is absolutely impossible, in treating of hemicellu- 

 loses, to draw any sharp dividing lines, for they are not only intimately 

 associated, but frequently chemically combined. Schulze (146) has 

 given the name paragalactan to the carbohydrate yielding arabinose 

 and galactose, which occurs in the seeds of many legumes. Winter- 

 stein (167) finds galacto-xylan in the water extract of Tropaeolum 

 majus, and numerous other examples of such combinations might be 

 cited. 



A class of substances to which has been given a distinctive name 

 because of their peculiar gelatinizing property, is the Pectins. As 

 Czapek^ remarks, "It is uncertain whether they form a definite 



^For further details see v. Lippmann; Chemie der Zuckerarten, Vol. I, pp. 160-169. 

 'Die Pektin-Substanzen; Czapek, Biochemie der Pflanzen, Vol. I, p. 545. 



