808 PHYSIOLOGY. 



that smell is due to the giving off of minute particles into the 

 air ; Morren, however, from observations on the flowers of 

 Orchids, was led to the inference that in some cases it 'depends on 

 a physiological cause. He observed that the aromatic odour of 

 Maxillaria, which continued to be exhaled as long as the flowers 

 were unfertilized, was lost a little while after pollen was applied 

 to the stigma. 



Though chiefly developed under the influence of solar light, 

 there are not a few plant-odours which are given oflf in the 

 evening or at night. Several Orchids, (Enothera, Lychnis vesper- 

 Una, and Ceretis graoidiflorus are examples. In the last-named 

 plant, the odour is given out in intermittent puflfs. 



There seems to be a connection between the colour of the 

 flowers and their odour ; thus it has been observed that white 

 flowers are very frequently fragrant, whilst brown and orange 

 ones have often a foetid smell, the so-called Carrion -flowers 

 (Stapelifs), certain Aroids, some Bcdanophorea, &nd the Rafflesia, 

 being examples. The flowers of Monocotyledons are more often 

 odorous than those of Dicotyledons. 



