330 DISEASES OF PLANTS. 



after drying; and certain woods, as Teneriffe rosewood, give out their 

 odour only when heated by friction. Meteorological causes have a 

 great influence on the odours of living plants. Dew, or gentle rain 

 with intervals of sunshine, seems to be the circumstances best fitted for 

 eliciting vegetable perfumes. Light has a powerful effect on the odour 

 as well as the colour of flowers. Plants, when etiolated by being kept 

 in darkness, generally lose their odour. In certain cases, the perfumes 

 of flowers are developed in the evening. Some of these plants were 

 called tristes by Linnasus, as Hesperis tristis, or night-scented stock. 

 Many orchidaceous plants are fragrant at night only, as some Catase- 

 tutns and Cymbidiums. Cestrum nocturnum and the white flowers of 

 Lychnis vespertina are also night-scented. The odours of some plants 

 are peculiarly offensive. This is the case with Phallus impudicus, and 

 with the flowers of many Stapelias. 



688. Schubler and Kb'hler, whose investigations in regard to colour 

 have been noticed, have also made observations on the odours of 

 plants in the same monocotyledonous and dicotyledonous orders. The 

 following tables show some of their results : 



Thus, of the plants examined, those having white flowers presented 

 the larger proportion of odoriferous species. The orange and brown 

 coloured flowers often gave a disagreeable odour. In examining 

 numerous species from various natural orders, they found that out of 

 100 species of 



Nymphseaceae 22 were odoriferous. 



Rosacese 13 



Primulaceae 12 



Boraginacese 6 



Convolvulacese 4 



Ranunculaceae. 4 



Papaveraceae 2 



Campanulaceae 1 



6. DISEASES OF PLANTS. 



689. Great obscurity attends this department of botany, and much 

 remains to be done ere a system of vegetable nosology (Wo-of, disease) 



