MISCELLANEOUS VEGETABLE PHENOMEKA. 79 



cases require a mordant to fix them, that they may not be 

 removed by wasliing. A mordant is any substance that 

 will unite with the coloring matter and with the fabric that 

 is to be dyed, and hold them united. We speak of it in com- 

 mon conversation as setting the d3'e, to prevent its fading. 



204. Besides the exquisite beauty of form and color, 

 Nature has furnished plants with iJerfume as varied as the 

 forms and hues of the corolla. The rose, violet, miguou- 

 nette, lemon, verbena, wcesachie, and a thousand others of 

 the flower garden and the lawn, owe their chief attraction 

 to the odor that distinguishes them. 



205. These perfumes proceed from oily or resinous mat- 

 ter contained in the receptacles of secretions. But how they 

 are liberated baffles investigation. 



206. Odors are of three kinds, permanent, ftigitive, a.nd 

 intermittent. Permanent odors are such as give out slowly, 

 and not only when living, but when separated from ' the 

 plant. They are more generally present in the wood and 

 bark, as the sandalwood, sassafras, etc. ; also in some flow- 

 ers and plants, as the rose, lavender, sweet clover, etc. 

 Fugitive odors are those that belong to transient organs, 

 such as leaves and flowers. These odors vary also with 

 the hour of the day, being generally stronger in the morn- 

 ing and evening than at midday. This of course is easily 

 explained. The heat dissipates the odor by excessive 

 evaporation; this being suspended in the evening, the 

 perfume accumulates, and when again rising is of course 

 stronger. Also at midday the current of air being up- 

 ward, the odors are wafted rapidly beyond us, while in the 

 evening the vapors settle, preventing their escape. 



207. Intermittent odors are more difficult of explanation. 



204. Have plants any other attraction besides form and color ? Odors proceed 

 from what ? 



205. Where is the oil and resin deposited ? Is the process of liberation 

 known ? 



206. How many kinds of odors are there ? Describe them. 



207. What of intermittent odors ? 



