MUCILAGE 



143 



arabic acid. ' The part soluble in water, when treated with 

 baryta water, gives two isomeric tragacanthan-xylan-bassoric 

 acids, which on hydrolysis yield a pentose sugar tragacanthose, 

 xylose, and bassoric acid C 14 H 20 O 13 . 



WOOD GUM AND CERASIN OR CHERRY GUM. 



These are pentosanes which occur in the wood of trees 

 such as beech, oak, cherry, ash, etc. ; they are extracted with 

 alkaline solutions, and on hydrolysis yield xylose. 



WOUND GUM. 



A gum-like substance, termed wound gum, is frequently 

 found in the tracheae of plants, in the immediate neighbour- 

 hood of wounds, and stopping up the lumina ; it is secreted 

 by the surrounding living cells. Wound gum does not swell 

 in water, and is insoluble in sulphuric acid and in caustic soda. 

 On oxidation with nitric acid it yields both mucic and oxalic 

 acids, and it responds to lignin tests ; e.g., on treatment with 

 phloroglucinol and hydrochloric acid a bright red coloration 

 results. 



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 Muscineae, Filices, and especially in the Phanerogams ; 

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

 AnthoceroS) Marattiaceae, some Cycadaceae, and Phanerogams ; 

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

 ginous ; e.g., ip. very many Algae, the hibernaculae 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. 



