90 SEGRETIONS. 



in a poisonous secretion, but no longer capable of dif- 

 fusing pestilence over an extensive territory. 



CAMPHOR, is obtained by distilling the wood and 

 bark of Laurus camphor a, and according to Sir Hum- 

 phry Davy, it exists in Sassafras, Marjoram and Sage. 

 Its properties and appearance are well known. 



The ELASTIC GUM, more frequently termed In- 

 dia rubber, is obtained from the Urceola, Jatropha, and 

 other trees of warm climates. When their bark is 

 wounded, it exudes in the form of a milky juice, which 

 becomes black in consequence of being dried in the 

 smoke. The fluid which exudes so abundantly from 

 different species of Silk weed Asclepias, is said to be a 

 variety of elastic gum. 



When wood is exposed to the action of an open fire, 

 it burns with a yellow flame, and disappears in the form 

 of vapour and smoke, or remains in the form of ashes, 

 but exposed to an intense close heat, it is converted 

 into charcoal. From the latter product, wood derives 

 its strength as timber, and its value as fuel ; the soil 

 its fertility, and the growing plant its food ; — but it can- 

 not with propriety be classed with the vegetable secre- 

 tions. The same remark is applicable to the alkalies 

 and earths which are found in the ashes of plants, and 

 in the soil by which they are nourished, constituting 

 an essential ingredient of both ; and formed with the 

 "primaeval mountains of the globe," but not as has 

 been fondly imagined, a product of vegetation. 



We have now examined the most important of the 

 vegetable secretions, and the examination is one of the 

 deepest interest. It has presented to our view the 

 root, absorbing from the earth, a tasteless, limpid, and 

 inodorous fluid, possessing the properties of mere wa- 

 ter ; it has enabled us to trace this fluid through an np 



