110 



BOTANICAL NOTICES OF NEW PLANTS. 



tribe is this circumstance more conspicuous than in the natural order Orchidacece. 

 All the species have curiously formed flowers ; some of them singularly grotesque ; 

 and though many of them are both elegant and highly coloured, a majority of 

 them are sombre -tinted, and lavishly spotted and chequered with dull purple, 

 muddy yellow, and lurid brown. These, however, notwithstanding their lugubrious 

 appearance, are finely scented, especially in the absence of strong light, a single 

 plant being sufficient to scent a whole building. 



Among many others of this interesting genus, the Cymbidium Sinensis is 

 remarkable for its symmetrical spike of dull yellow flowers, and powerful fragrance 

 in the dark ; and there are several other species equally odorous and equally 

 destitute of vivid colours. 



But why should dull- coloured flowers evolve a higher or more powerful aroma 

 during night than by daylight ? Is it because their excretion of nectar or honey 

 is more copious in the night season than it is by day, in consequence of the dull 

 petals imbibing more heat in the day than if they were of a lighter hue ? or is it, 

 that the effluvia are less volatile in the denser air of night than in the rarer air of 

 day, and therefore less sensibly perceived by . day visiters ? These are questions 

 which we dare not venture to answer ; but we recommend the circumstance as a 

 curious incident among the phenomena of vegetation. 



We know not whether the scent evolved from flowers is in any way connected 

 with colour. It is the qualities of their juices which acquire colour from the 

 action of the sun's light. This coloured juice is termed the chromule ; and 

 according as this is more or less in quantity, the colours are deeper or paler. 

 One class of tints are said to be oxidated, and another de-oxidated. All modifi- 

 cations of the coloured matter occasioned by its oxidation cause the great variety 

 of colour exhibited by plants. 



It is said that the leaves, and no doubt the flowers also, exhale oxygen gas in 

 the day, and absorb it during the night. Is it probable that the inhalation of 

 this gas displaces that odorous vapour so amply diffused by the plants alluded to 

 in the night % Whatever may be the cause, there can be no doubt of the fact, 

 that brown-coloured flowers are most odorous during night ; and as it is a subject 

 which has not yet been satisfactorily explained, deserves the attention of every 

 studious botanist. 



BOTANICAL NOTICES OF NEW PLANTS. 



DICOTYLEDONES. 



RHODOEACEiE. 



Rhododendron albiflorum. Hooker. White-flowered Rhododendron. Bot. Mag. t. 

 3670. This is not a showy, but a very distinct species, bearing delicate cream-coloured flowers. 

 It was discovered by Mr. Drummond, in the Alpine woods of the Rocky Mountains ; and seeds 

 which were sent by the officers of that expedition to Dr. Graham, produced plants which 

 blossomed in July 1837. Bot. Mag. 



