208 NUTRITIVE PRODUCTS OF PLANTS. GUM. 



substance to man and animals ; and it forms an important article 

 of diet in Arabia and Senegal. Those who are engaged in col- 

 lecting it live for a time almost entirely upon it ; and six ounces 

 have proved sufficient to support an adult for 24 hours. It is on 

 record that a caravan crossing the Desert, their provisions being 

 exhausted, preserved themselves from famine, by eating the Gum 

 Arabic, which formed part of the merchandise they were trans- 

 porting. But no animals could continue long to subsist on this 

 ingredient alone ; since it contains no nitrogen, which is still more 

 essential to their support, than to that of plants. (See ANIM. 

 PHYSIOL. . 155157.) 



329. Gum is almost the only organic substance, that seems 

 to be immediately applied to the nutrition of the plant, when 

 absorbed from without, instead of being first decomposed into 

 water and carbonic acid; for a plant thrives well in a solution of 

 it. This is evidently, because it thus supplies an important ingre- 

 dient in the ascending sap, in which it would otherwise have to 

 be formed. (. 317- ) The gum contained in the elaborated sap 

 appears to have undergone some change, which renders it more 

 prepared for being converted into an organised tissue. It is this, 

 which, being poured out between the bark and the newest layer 

 of wood, is the viscid substance termed cambium; in which the 

 rudiments of the cellular tissue, that is to form part of the new 

 layer of wood, after a time present themselves. Even if this 

 cambium be drawn off from the stem, its particles show a tend- 

 ency to arrange themselves in a form resembling that of cells and 

 vessels j though no perfect tissues are produced by this kind of 

 coagulation. The interior of young seeds is filled with a glu- 

 tinous pulpy fluid of a similar description ; and partitions gra- 

 dually appear in this, converting it into a mass of cellular tissue. 

 Ordinary Gum may be considered as having the same character 

 in the Plant, as Albumen possesses in the Animal ; being the raw 

 material, at the expense of which the tissues are ultimately 

 formed. But this peculiar organisable Gum is evidently analo- 

 gous, in its tendency to become organised, to the Fibrin of 

 Animal fluids. (ANIM. PHYSIOL. . 16 19.) 



330. If a wound be made in the bark, a similar glutinous 



