GUMS AND MUCILAGES. 29 



GUMS AND MUCILAGES. 



In the gradual anabolism of plants there are built up 

 numbers of bodies that are very closely allied one to 

 another, and which are intimately related to the carbo- 

 hydrates. Among these carbohydrates are some charac- 

 terized by their relatively easy solubility in water and 

 showing certain definite chemical reactions, notably the 

 reaction toward saturated aqueous solutions of potassium 

 acetate. The precise method of the histological formation 

 of gums is still a matter of a great deal of controversy.* 



Practically all the varieties of gum are characterized 

 by their insolubility in alcohol, ether, or chloroform; and 

 when heated with dilute sulphuric acid they are con- 

 verted, for the most part, into simple sugars, glucoses, 

 of the pentose (CgHjoOg) and hexose (CJi^fi^) groups. 



In form they are not identical, but are usually roundish 

 to elongated or root like or in tears, and only in rare in- 

 stances have they characteristic shapes. Most gums show 

 surface cracking ; for instance , acacia . They usually have a 

 sharp fracture when dry. In color they vary from white 

 through various shades of yellow to brown. They are 

 mostly translucent or transparent, some of the darker 

 varieties being opaque; they have for the most part a 

 glassy surface, at least in the broken surface. They 

 are odorless, usually mucilaginous, sweetish or bitterish 

 to taste. Many are markedly hygroscopic and tenacious, 

 thus rendering it difficult to powder them. 



They vary very widely as to their solubility — all will 

 dissolve somewhat — when placed in water; some are 

 readily soluble, others insoluble. Most gums possess the 

 interesting property of being soluble in concentrated 

 aqueous solution of chloral hydrate. 



♦Tschirch: Ueber die Entwickelungfsgeschichte einigcr Secret- 

 behaltcr und die Genesis ihrer Secrete. Bcr. d. Deut. bot. Gesellsch., 

 1888. S. 2. 



