ODORS. 135 



cut-flower, that it gave off puffs of odor every half hour, from 

 8 to 12 P. M., when it faded, and the smell became very slight. 

 On another occasion, when the flower was left on the plant, it 

 began to expand at 6 P. M., when the first fragrance was per- 

 ceptible in the green-house. A quarter of an hour afterward 

 the first puff of odor took place, after a rapid motion of the 

 calyx ; in rather less than a second quarter of -an hour, another 

 powerful emanation of fragrance took place; by 35 minutes 

 past 6 the flower was completely open ; and at a quarter to 7 

 the odor of the calyx was the strongest, but modified by the 

 petals ; after this time the emanations of odor took place at the 

 same periods as before." 



Many other cases might be cited of singular phenomena, 

 properly coming under this head. The odors in these cases are 

 certainly developed or emitted on different principles, in the dif- 

 ferent cases under this variety. The explanations are entirely 

 beyond our reach. There seems to be a specific action of the 

 organs for the production of the odors, as there can be no glands 

 discovered by which the odorous fluid is secreted. That the 

 odorous fluid is emitted as it is generated, which of course must 

 be periodically, is rendei'ed probable by the fact, that emission 

 of carbonic acid took place in the same manner from the flower 

 of the Cereus. 



255* Odors have also been classed, from their similarity of 

 effect on the human system, into aromatic, stimulating, penetra- 

 ting, and sweet, but the difficulty of fixing definite limits to the 

 application of these terms renders the classification of little use. 



256. Schuhler and Kohler have made many interesting ob- 

 servations on odors as well as colors. They found that, of the 

 various colors of flowers, some are more commonly odoriferous 

 than others, and that some colors are more commonly agreeable 

 than others. 



Color. No. of species. Odoriferous. Agreeable. Disagreeabla. 



White 1193 187 175 12 



Yellow 951 75 61 14 



Red 923 85 76 9 



Blue 594 31 23 7 



Violet 307 23 17 6 



Green 153 12 10 2 



Orange 50 3 12 



Brown 18 10 1 



The white most odoriferous and agreeable, the yellow^ and brown 

 most disagreeable. 



2^5. How have odors been classed ?— 256. AVliat did Schublcrand Kohler 

 find Willi re;,'ard to the relation of color to odor ? What color most odor- 

 iferous ? Which most disagreeable ? 



