4 
ON THE PERIODICAL EMISSION OF THE ODOURS OF PLANTS. 
ture; and if the roots are much matted, pick them ont a little with a sharp pointed stick, so as to give 
them a chance of entering at once into the new soil. In potting, press the soil, especially if dry, very 
firmly; so firmly that the thumb, if pressed upon it, after watering, will scarcely leave an impression. 
The sticklers for porosity, mechanical action, and so forth, may object to this firm potting; and indeed 
the plants will not grow so rapidly in it as in porous potting; but they will make more healthy growth, 
and live a much longer time. After the plants are potted, place them in a frame or pit, water occa¬ 
sionally as required, until the whole mass of soil is moistened, and keep them tolerably close, and 
the atmosphere moist, until the plants get into free growth, when abundance of air must he admitted. 
The plants must now be considered as fairly started, and their subsequent treatment must form the 
subject of another paper.—A. 
- ♦- 
ON THE PEEIOLICAL EMISSION OE THE OLOHES OE PLANTS. 
f T is a well-known fact that many plants give off the most powerful perfume in the evening and 
night-time. This phenomenon has been attributed to various physical causes, arising out of 
peculiar conditions of the atmosphere, &c.; but little is known on the subject, and some observations, 
published several years ago by Professor Morren, seem strongly opposed to any physical explanation 
of the facts. It had been supposed that flowers merely gave out the more powerful odour at 
night on account of the volatile perfume- being less quickly dissipated at that time than when the 
sun was above the horizon. It was also a question whether the condensation of the atmosphere 
during the night might not be the cause of the increased power of the scent. Orchis bifolia occurs 
abundantly about Liege in spring, and its white flowers, which are quite scentless during the 
day, give out a pleasant, penetrating aroma in the evening, and especially about eleven o’clock at 
night. Professor Morren convinced himself by five days’ observation that the perfume began to be 
manifested at twilight, exhibited the greatest energy at the time when the darkness of night 
prevailed, and decreased with the dawn. Two spikes of flowers of this Orchis were placed in two 
cylindrical glasses filled with water, in which the plants were totally submerged. One glass was 
placed so that the sun might shine upon it all day, the other was kept in the shade. Any scent 
emitted from these flowers could only be perceived through the water by which they were covered. 
As evening came on a delicious aroma became evident, and was emitted throughout the night, being 
lost at sunrise. This proves, says Professor Morren, that the condensation of the vapour has not the 
slightest influence upon the perception of the odoriferous constituents by our senses. It further proves, 
in regard to the plants exposed to the air, that neither the evaporation of the particles nor the accumu¬ 
lation of them on the parts of the plant where they have their origin, is the cause of the periodical 
absence and recurrence of this exhalation ; so that the explanation of this phenomenon must 
undoubtedly be sought in physiological facts. 
Professor Morren made another experiment. The blossom of Maxillaria aromatica is well known 
for its strong odour of cinnamon, so that two or three flowers will scent a whole conservatorv. And it 
is well known that in the fertilization of the Orchideae, the deposition of the pollen on the stigmata is 
effected very quickly, that the pollen-tubes elongate in less than one hour, the flowers and the 
perianth begin to close, and the columella shoots up. In a plant bearing many flowers, examined bv 
Professor Morren, the scent was strong, penetrating, agreeable, and resembling fine cinnamon. The 
unfertilized flower retained this odour day and night, morning and evening, for eight days. Each 
flower that was fertilized by Professor Morren lost its odour in half-an-hour after the operation, and 
ne\ er ga^ e further signs of it. This fact seems alone sufficient to prove that the emission of the odour 
is a vital phenomenon. 
This is a subject upon which good and careful observations are still requisite.—A. H. 
