478 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



rule produced by the action of enzymes, and that mucilage substances may arise 

 in this manner is shown by the formation of dextrin during the hydrolysis of 

 starch. Indeed gelatinous or mucilaginous substances often arise as intermediate 

 products of the action of cellulose ferments'. The gummy modification of 

 cell-walls is also probably caused by the action of a ferment, although none such 

 has as yet been isolated, nor even its existence demonstrated 2 . Similarly ' pectase ' 

 is the problematic ferment which in the presence of calcium salts induces the 

 decomposition of pectins with a formation of insoluble calcium pectate 3 . 



As might be expected, the different substances mentioned are used for a 

 variety of purposes : thus gelatinous materials take part in the formation of the 

 cell-wall, in which pectins are perhaps always present (Sect. 83), and not only 

 the gelatinous reserve-celluloses, but also the mucilage dissolved in the cells of 

 orchid-tubers, rhizomes of Symphytum, &c. *, serves as reserve food-material. 

 Pectins may perhaps often function as plastic material, although it is doubtful 

 whether the marked diminution in the amount of pectins during the ripening of 

 fruits 5 is due to their being converted into sugar, &c. 



The aplastic mucilaginous substances which remain permanently present in 

 the cells or in special receptacles are probably for the most part of biological 

 importance. Thus they may afford a certain protection against injury or the 

 attacks of animals, while in other cases the mucilage may serve for the first 

 attachment of seeds (Mistletoe, Linseed). It has moreover already been shown 

 (Sect. 38), that mucilage in spite of its feeble osmotic power may serve in other 

 ways to check transpiration. 



Further details will be found in the literature quoted, and the manner in 

 which these substances may be classified will differ according to whether a 

 morphological, functional, or biological standpoint is adopted. Cf. De Bary, 

 Vergleichende Anatomic, 1877, pp. 86, 150, 210; Tschirch, Angewandte Pflanzen- 

 anatomie, 1889, p. 204; Walliczek, Jahrb. f. wiss. Bot, 1893, Bd. xxv, p. 209; 

 Schilling, Flora, 1894, p. 280; Mangin, Bull. d. 1. Soc. Bot. d. France, 1894, 

 T. XLI, p. xl ; Haberlandt, Physiol. Anat., 1896, 2. Aufl., p. 439, and the literature 

 quoted in these works. 



Fats. Every protoplast appears to contain small amounts of fats (Sect, n), 

 even although owing to its fine state of sub-division or to its existence in com- 

 bined form it may be invisible until it is caused to coalesce and appear as little 

 droplets*. This takes place whenever a large quantity of fat accumulates, which 

 is a frequent occurrence. Fats serve as reserve food-material not only in numerous 



1 Cf. Griiss, Bibliotheca hot., 1896, Heft 39, p. 7, and Sect. 91. 



3 Wiesner, Sitzungsb. d. Wien. Akad., 1885, Bd. xcn, p. 40. Cf. also Reinitzer, Zeitschr. f. 

 physiol. Chemie, 1890, Bd. xiv, p. 453. 



8 Bertrand et Malleve, Compt. rend., 1895, T. cxxi, p. 726 ; Maumene, ibid., 1894, T. CXIX, 

 p. 1012. 



4 Frank, Jahrb. f. wiss. Bot., 1866-7, Bd. v, pp. 181, 196; A. Meyer, Archiv d. Pharm., 1886. 



5 See Chodnew, Ann. d. Chem. u. Pharm., 1844. Bd. LI, p. 392, and the literature on the 

 ripening of fruits in Sect. 109. 



' Hofmeister, Pflanzenzelle, 1867, p. a. 



