31-^ 



PLANTS PRODUCING GUMS AND RESINS 



nut be confused with metagummic acid, although to a certain 

 extent analogous with this latter. 



Several theories have been enunciated as to the formation 

 of giuii in plants; Trecul has attributed it to an over- 

 nutriti(jn of the cells; Beijerinck regards it as tiie action of 

 certain bacteria or even of a Pyrenomycetes, Plcospora giim- 

 mipara; Wiesner believes that this transformation is due to 

 the action of a soluble ferment, of a diastase turning cellulose 

 into gum and starch into dextrine. What is acknowledged 

 and what usually happens is that the gum arises from the 

 gelilication of the cellular membranes of the stems and 

 branches of certain plants. This substance filters through 

 the natural, chance interstices between the tissues to the 

 surface of the bark, where it gathers in mammillated masses 

 of varving hardness. 



Gummiferous plants usually exude their gum in the dry 

 period which succeeds the rainy season ; they occur more 

 especially in barren and sandy countries. 



M. L. Mangin, basing his view on the composition of 

 the cell, which, in addition to cellulose, contains pectic com- 

 pounds (pectose and pectic acid), considers that true gums 

 have the same colouring reactions as these pectosic muci- 

 lages, whilst mixed gums behave lik'e. mixed mucilages in the 

 presence of colouring reagents. 



The following classification is bv Cooke : — 



True Gums 



or 



Pectosic Gums. 



[a] True gums which are soluble. 

 Example : Gum arable, Gum Sene- 



\ gal. 



[b] True gums partially soluble. 

 Example : Cherry-tree gum. 



Gum tragacanth. 



II. 



Mixed Gums 



or , 



Pseudo Gums, i 



III. ^ 



Tanniferous Gums , Gum of Butea, Pterocarpus, &c. 



or Kinos. j 



