ODORS. 133 



circumstances, exhibits it. Some, nearly scentless otherwise, 

 become strongly odorous when rubbed or heated. The Pine, 

 Oak, and Beach, are examples of this kind. Others are odorous 

 for a long time after being cut, under ordinary circumstances ; 

 of this kind are the Rosewood of Teneriffe, the Cedar and Sandal- 

 wood (Santalum album) of India, so highly esteemed in Eastern 

 Asia for its fragrance. The slight volatility of the oil, to which 

 these species owe their odors, and the compactness of the wood, 

 enable them constantly to yield their fragrance for an indefinite 

 length of time. 



250« Others are fragrant when first cut, but lose this property 

 in a very short time, as is the case with the Cinnamon and 

 Cassia, the fragrant substances being volatile, and the wood 

 porous, both causes concurring to render the wood in a short 

 time scentless. 



251. Fugitive odors are such as belong to organs of short 

 duration, as the leaves and flowers, and we meet with them in 

 the greatest abundance, and most frequently in the latter. All 

 are aware that the flower is the source whence flows the delight- 

 ful fragrance of the flower garden ; and during the season of 

 bloom of our Magnolias, the woods and swamps are perfumed 

 by the odor of their flowers. It must have been remarked also, 

 by the most heedless observer, that the odor of the garden, or 

 forest of Magnolias, is much more pungent at some parts of 

 the day than at others. During the direct action of the mid- 

 day sun, little or no perfume is perceptible from either ; but as 

 the sun sinks to the horizon, and the dews begin to settle on the 

 leaves, the evening air becomes scented with their fragrance. 

 The odor accumulates during the night, and as the dew begins 

 to exhale with the rising sun, it is borne on the air in much 

 greater abundance than at any other hour. Thus these silent 

 worshipers pour forth their incense in a morning sacrifice to Him 

 who extends to them, as to all, his kind regards. 



A shower produces similar effects. Who has not enjoyed the 

 grateful odor exhaled from the flowers of the field or garden 

 after a summer's shower ? 



252. The causes of these apparently great emissions of odor, 

 under the circumstances mentioned, and the apparent suspension 

 of their emission, have not been satisfactorily determined. It 

 has been supposed that the heat of mid-day, under the direct 

 action of the sun's rays, produces so much evaporation as to 



250. How with cinnamon and cassia? — 251. What are fugitive odors? 

 When is the odor the strongest? What effect has a shower?— 252. How 

 *r« the above phenomena explained ? 



