Proceedings of the Linnean Society of London - University Library

46
PROCEEDINGS OF THE
how the legumiuous phmts restored the soil, and no doubt there
is still much to be discovered regarding it.
Virgil mentions the lupin as a field-crop, we only know it as a
flower grown for ornament ; but to the present day in Germany
lupins are grown very extensively on very poor soil every third
or fourth year, simply to be ploughed in to enrich the soil ; the
lupin is so bitter that no animal will eat it, but sometimes it is
used in Germany as bedding for the cattle. The lupin ILiqnnus
luteus, Linn.] thus grown has a yellow flower.
February 19th, 1903.
Some Eemarks on the possible Uses of Essential Oils in the
Economy of Plant-life. By Dr. Geokge Henderson, E.L.S.
Everybody knows that moisture in the air tends to prevent
frost at night, but it is not always realized that the moist air, even
when clear and when there are no clouds, still acts in the same
way, and stops radiation from the surface of the ground.
Professor Tyndall, thirty-two years ago, experimenting on this
subject (see his ' Fragments of Science '), found that infinitesimal
quantities of essential oils in the air enormously increased its
power of absorbing heat-rays of low tension.
I am not aware that anyone has applied this fact as serving any
useful purpose in plant-life, but it seems to me that in this way
these oils may often prevent injury from frost at one of the most
critical periods of the plant's life, namely, Avhen it is setting its
fruit.
In the low hills of the Punjab Himalaya, from 1000 to 4000
feet above the sea and 10 to 20 miles across, in the end of March
and in April, when most of the plants are coming into flower, the
blossoms are apt to be blighted by late frosts, at least one would
expect this ; but at that season the air is filled with the odours of
essential oils from these blossoms to such an extent as to be at
times (and especially on a still night, when frost most often occurs)
quite overpowering.
My theory is that these essential oils help to prevent radiation
at night, and thus preserve the blossoms and allow the fruit to set
after all, it is usually only a matter of four or five degrees' fall of
temperatui'e just at sunrise which does all the damage.
I mention the Punjab Himalayas because it was there the matter
first attracted my attention, and probably nowhere else is there
more risk of damage from late fi'osts.
Tyndall states that, taking the absorptive power of dry air at 1,
moisture added to the air increases this power to 72 ; but an
infinitesimal trace of
Oil of Eosemary gives 74
Oil of Laurel
"
„
80
Camomile flowers ,, 87
Cassia „ 109
Spikenard ,, 355
Aniseed „ 372
;