PLANTS PRODUCING GUMS AND RESINS 313 



What should be the quahties of a gum ? 



Firstly, it should be as devoid of coloration as possible, 

 soluble in water, yieldino- a mucilaginous liquid, spreading 

 and adhesive ; it should then be free from an\' admixture 

 and devoid of an^- blemishes such as fragments of bark, 

 leaves, &c. 



In order to conform with trade requirements, M. de 

 Cordemoy says it is important that gums should fulfil the 

 following conditions : — 



(i) A sample should contain a single kind only, derived 

 from one and the same plant. 



(2) The product should be of a pale colour, clear and 

 homogeneous. 



(3) The admixture of foreign substances should, as far 

 as possible, be avoided. 



(4) A good gum should be tasteless and odourless, and 

 should form tasteless and odourless solutions, or at any rate 

 its taste and smell should not be disagreeable. 



The extraction of the Qum beo-ins at the end of the rainv 

 season. Usually, in order to facilitate exudation, after the 

 bark has been scraped and cleaned to prevent any fragments 

 dirtying the product, longitudinal incisions are made in the 

 stem. As true gums are formed in the soft tissues exterior 

 to the ligneous zone of the stems there is no need for these 

 incisions to be deep. 



RESINS. 



It is generally considered that resins are derived from 

 the oxidation or hydration of essences or essential oils. 

 These essential oils pour out of the cells which form them 

 into the secretory canal. Thev are converted, according to 

 their degree of oxidation, into oleo-resin if oxidation is 

 partial and into pure resin if oxidation is complete. In the 

 latter case the mass becomes solid. 



Balsams are liquid resins, containing in the free state 

 cinnamic or benzoic acid or both, and resins. 



