I90 THE CARBOHYDRATES 



produced either by over-nutrition of certain cells or by 

 bacterial action ; * according to Wiesner, all gums are pro- 

 duced by a diastatic ferment acting on cellulose ; although it 

 is not possible to express any definite views on the subject, 

 it would appear not improbable that in many cases the 

 formation of gums and gum-like substances in the plant is 

 a morbid condition. Mohl was able to show in the case of 

 tragacanth gum that this substance was produced by the 

 metamorphosis of the cells of the medullary rays. 



MUCILAGE. 



The term mucilage is applied to those substances which 

 with water produce a slimy liquid. Mucilage is widely dis- 

 tributed, and occurs in all or nearly all classes of plants. 

 Mucilage-secreting hairs, or comparable structures, occur in 

 various Muscinese, Filices, and especially in the Phanerogams ; 

 mucilage sacs or canals are found in certain Muscineae, e.g. 

 Anthoceros, Marattiaceae, some Cycadaceas, and Phanerogams ; 

 further, the external walls of plants may be generally mucila- 

 ginous ; e.g. in very many Algae, the hibernaculas of some 

 aquatic Phanerogams, like Utricularia and Myriophyllum, and 

 finally in the coats of seeds and fruits, such as Lepidium and 

 Sterculia scaphigera respectively, in which cases the superficial 

 cell walls are mucilaginous. Mucilage is not infrequently 

 associated with other substances ; thus in the case of mucilage- 

 secreting hairs, it is sometimes associated with tannin, and in 

 many plants, especially in the mucilage sacs of many Mono- 

 cotyledons, calcium oxalate is found. 



Employed in the morphological sense the term mucilage 

 includes a number of chemically distinct substances ; thus 

 while the mucilages from linseed, many of the Liliacese, and 

 also salep yield only sugars on hydrolysis, many of the mucil- 

 ages contained in seaweeds yield in addition to sugars, ash 

 constituents which, previous to hydrolysis, were chemically 

 combined with the carbohydrate residue. The high sulphate 

 content of the ash of carragheen mucilage f (obtained from 



* See Greig Smith : " J. Soc. Chem. Ind.," 1904, 105, 972. 

 t Haas and Hill : " Ann. App. Biol.," 1921, 7, 352 ; Haas, " Biochem. 

 Journ.," 1921, 15, 469. 



