144 THE CARBOHYDRATES 



The constitution of mucilages is as yet unknown ; they 

 are, however, related pretty closely both to cellulose and to 

 arabin. In fact, by some authors they are regarded as de- 

 composition products of cellulose, produced either by over- 

 nutrition of certain cells or by bacterial action ; * according to 

 Wiesner, all gums are produced 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. 



That mucilages are not all of the same constitution is 

 shown by the fact that the mucilaginous substance obtained 

 from Fucus (caragheen mucilage) on hydrolysis with dilute 

 sulphuric acid yields galactose, while salep mucilage, obtained 

 from Orchis Morio, on a similar treatment yields mannose. 



Function. 



Mucilage, when it is a definitely secreted product or of a 

 definite and constant occurrence in a plant, may perform several 

 functions, but how far these are primary functions cannot yet 

 be stated. 



When it occurs in tubers, as in the Orchidaceae, mucilage 

 is generally looked upon as a reserve food-material ; it may 

 serve as a check against too rapid transpiration, especially 

 when produced in connexion with developing organs, such as 

 vegetative buds, young leaves, in the epidermis of mature 

 leaves, the sporangia of Cryptogams, etc. ; in the case of 

 aquatic plants, such as Algae, the hibernaculae of Myrio- 

 phyllum, etc., its presence may prevent a too rapid diffusion ; 

 the calcareous incrustation of certain Algae, e.g., Neomeris 

 dumetosa, is dependent on the presence of mucilage ; mucilage 

 provides a water-storage mechanism in plants subjected to 

 xerophytic conditions, e.g., Cassia obovata, Malva parviflora, 

 Theobroma cacao^ and Pterocarpus saxatilis ; finally, it may be 

 an important aid -in connexion with seed-dispersal and ger- 

 mination, as in some species of Salvia and Lepidium. 



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



