274 Mary Davies Swartz, 



class of cell wall substances, or whether they should be classified 

 as 'hemicelluloses' or 'pentosans.' " In 1868, Scheibler (141) found a 

 sugar which he called pectinose, but which was later shown to be ara- 

 binose (142). In 1875, Reichardt (132) obtained a pectin body from 

 carrots and beets, which he called 'pararabin,' expressing the view 

 that pectins should hardly be considered as a special class of carbo- 

 hydrates. Tromp de Haas and ToUens (160) have found from numer- 

 ous analyses, that the pectins do not differ from other carbohydrates 

 in their relative proportions of hydrogen and oxygen so much as earlier 

 workers supposed, and hence they may be classified with other hemi- 

 celluloses according to the products of their hydrolysis (pentoses; 

 galactose and other hexoses). Cross (106) believes them to be allied 

 to the ligno-celluloses. The whole matter is still in a state of uncer- 

 tainty. Herzfeld (116) has shown that arabinose can be obtained 

 from most pectins, and consequently they have been included among 

 the pentosans, though from the frequency with which they yield ga- 

 lactose, they might equally well be discussed with the galactans. Ac- 

 cording to Czapek while pectins occur frequently in phanerogams, 

 ferns and mosses, their presence in algae is doubtful, although it is 

 possible that soluble carbohydrates of algae yielding arabinose or ga- 

 lactose are closely related to the pectins of other plants. ^ 



Role of the Pentosans in Plant Physiology. 



Comparatively Uttle is known of the role of pentosans in plant phys- 

 iology. De Chalmot's (108) observation that they decrease in quan- 

 tity in seeds — peas and corn — during germination, and reappear 

 in the stems and roots of the growing plant, would seem to indicate 

 that they form a part of the reserve material in the seed; but Schone 

 and Tollens (145), finding no diminution in the amount of pentosans 

 in grains during germination, but rather a slight increase, declare that 

 they do not belong to the reserve-stuff of the seed ; so the question may 

 be regarded as still unsettled. Changes in the relative amounts of 

 pentosan in plants at different stages of growth, studied by Cross, 

 Bevan and Smith (105), Gotze and Pfeiffer (113), Calabresi (98), and 

 others, show that the increase of pentosans runs parallel to the forma- 

 tion of the skeletal substance ; and have led to the idea that they arise 

 through the transformation of a part of the cellulose, and along with 

 lignin and cutin, take part in wood formation. Ravenna and Cereser 



^Cf. also Bigelow, Gore, and Howard (92). 



