SCIENCE OE GARDENING. P art II.
violet end, increases from that to the red extremity : and when the thermometer was
placed beyond the limit of the red ray, it rose still higher than in the red ray, which has
the greatest heating power in the spectrum. The heating power of these invisible rays
was greatest at the distance of half an inch beyond the red r a y ; but it was sensible at
the distance of one inch and a half.
1343. The infiuence o f the different solar rays on vegetation is not yet thoroughly understood;
but it is quite evident that the heating and the dlumiuating rays produce
different effects. “ Chemical action,” observes Professor Solly, “ is caused in the cells
of the leaves by the agency of these chemical rays of light, which enable the vital power,
as it is called, to form organic ma tte r; hence it is frequently said that light stimulates
vegetation. Chemical action is also augmented by heat, which, though it cannot alone
effect those changes usually produced by light, considerably assists them, and is, therefore,
classed with light as a stimulus.” (liural Chemistry, 2nd ed., p. 153.)
1344. The three properties o f light have been defined by Mr. Hunt as producing colour,
heat, and actinism or chemical action ; and in a paper read before the Society of A its
on the 16th of February, 1848, he endeavoured to explain the principles on which tinted
glass has been adopted in some liothouses. According to his theory, it appears that
the full action of the chemical rays was secured by the use of glass stained blue by
cobalt; that the hot rays were best obtained by the use of red glass ; and that yellow
glass abstracted the chemical and heat-giving rays without impeding those which contained
only lig lit; and, therefore, “ when tliere was any tendency to form too much
stalk or leaves, aud it was desired to produce more wood, it was done by admitting as
much light as possible, with the smallest possible quantity of actinic power, and that
might be effected by interposing glass of a yellow tint.”
1345. Whatever may be the cause o f the influence which light lias on vegetation, there can
be no doubt that it is vciy considerable. Thus, plants kept in darkness, but supplied
with heat, air, and moistui-e, groiv for a short time, but they never gain thcir natural
colours; their leaves are white and pale, and thcir juices watery and peculiaidy saccharine.
Sect. II. O f Electricity.
1346. Electrical changes are constantly taking place in nature, on tho surface of the
earth, and in the atmosphere; but, as yet, the effects of this power on vegetation have not
been coiTectly estimated. It has been shown by experiments made by means of the
voltaic battery, that compound bodies in general are capable of being decomposed by
electrical powers; and it is probable that the various electrical phenomena occmi'ing in
om- system must influence both the germination of seeds and the growth of plants. It
has been found that seeds have sprouted much more rapidly in water positively electrified
by the voltaic instrument, than in water negatively electrified; and experiments made
upon the atmosphere show that clouds are usually negative ; and, as, when a cloud is
iu one state of electricity, the surface of the earth beneath is brought into the opposite
state, it is probable that in common cases the sm-face of the earth is positive. A similar
experiment is related by Dr. Dai-win. (Phytologia, sect. xiii. 2, 3.)
1347. Respecting the nature o f electricity, different opinions are entertained among
scicntiflc men. By some, the phenomena are conceived to depend upon a single subtile
fluid in excess in the bodies said to bo positively electrified, and in deficiency in the
bodies said to be negatively electrified; a second class suppose the effects to be produced
by two different fluids, called by them the vitreous fluid and the resinous fluid; and
others regard them as affections or motions of matter, or an exhibition of attractive
powers similar to those which produce chemical combination and decomposition, but
usually exerting their action on masses.
1348. A profitable application o f electricity to promote the growth of plants has not yet
been discovered; though it has been a favourite idea with naturalists for more than a
ccntm-y. The following brief account is abridged from a paper on the subject by
Professor SoUy (published in the Journal o f the Horticultural Society o f London). The
earliest experiments” on the subject appear to have been those of Dr. Maimbray of
Edinbm-gh in the yeai- 1746, when he electrified two myi'tles during the whole month
of October, till at length they put forth fresh branches and flowers. In 1747 a paper
was read before the Royal Society on the effects of Electricity on Vegetables, and many
experiments were tried in England, France, and Germany on the subject; but they do
not appear to have been attended witb much success, as we find no experiments of any
importance recorded for the *next tliii-ty years, though Priestley, Du Hamel, Bcccaria,
and others, alluded to the subject in their wa-itings, and mentioning the rapid growth
which has been observed in plants during a thunder stoi-m, suggested the idea of trying
experiments on a large scale. We do not, however, find any important experiments
recorded till 1779, about eleven years after Priestley published his History o f Electricity.
In that year the Count de Laccpedc published an account of some experiments whicli he
Book II. THE ATMOSPHERE. 431
Ions plan was, that he proposed to irrigate tlie ground in wliich the nlants were to ha
while jt vvas c l e c S d ! ' P nSed iS efyTfÜ ^^ ^ ' S i S i o n ^ o f ' S
electnc. y on yegetation. Ho eridontly liimself bolioyes that it has s L r e f f i c L ZiTo
Do CandoUe appeai-s to he of a contrary opinion. Sfr Hirniplny Davy S i P o S
riionai-s, Bcoqnerel and Dutrodiot, also tried e"xperimcnts on f tH L i c c T h n te itZ ,
predncmg any marked rcsnlt. “ In the spring of 1843,” sayT P iL S s i Solh
interest was exeited by the statement whicii tiren became c u L n t, t e T l dZcoréiT L d
been made of a means of coUecting tlie natnral elcctiicity of tli! a tiL L lm T rsT as to
inciease yegetation in a most extraordinary manner. TUo statement on wliicli this
i r d d d’’' ? founded originated witli Dr. Forster, of Kndrassie, Elgin- who liavino-
stretclied certain lyu-cs in particidar directions oyer a crop of barley, had ohsorvcd a most
luxunant yegetation produced. About-the same tinS aecouuTs of soZe C e “ 7
experiments were cn-culated, from wliieli it appeared that eqnaUy ex trao iU frA X L
c X ’Z X Z Z «f OtofeLs of y o ltX e L L tZ
city. (Journ. Hort Soc., yol. i. p. 99.) In consequence of those statements exneriinents
were made in yarions parts o f th e country, and particularly ta
Horticnltmul Society at Chiswick, and in those of the Botanic^ SocieL i f the EegeTL
d iy th e 'i 9nses the result was a complete faUiire. In most places tlie crop was
exactly the same as other crops on tho same ground without any electricity and where
wiL X o Z n t a T lL r é ‘“ft ft'ftft“'“ “ ft™P®- ™P«™ents
Sect. HI. O f TFaier.
^ 1349. IFaiei- is a compound o f oxygen and hydrogen gas, though primarUy reckoned it
simple or elementaiy substance. “ I f the metal caUed potassimn be exposed in a glass
tube to a small quantity of water, it will act upon it with great violence- elastic fluid
Z d be found to be hydrogen; aud the same effects wiU be
pi oduced upon the potassium, as if it h.ad absorbed a small quantity of oxygen- and the
hydrogen disengaged and the oxygen added to the potassimn, are in weight as 1 to 8-
S 1 f f e f f t , ft “f “ T " ’ot 1 and 8, he introduced mto a c?lo“se ° v"efts sel, and an electrical spai-k Apass ethde twlue-oLiiho-th!
them, they wiU inflame, and condense into 9 parts of pnre water.” “
1350. Water is absolutely necessary to the economy o f vegetation in its elastic aud fluid
states; and it is not devoid of use even in its solid form. Snow and ice are bad conductors
of heat; and when the ground is covered with snow, or the surface o fth e soil or
of watci IS frozen the roots or bulbs of the plauts beneath are protected by the congealed
water ii-om the mflnence of the atmosphere, the temperature of wliich, in northern wfiitci-s
IS usually very much below the freezing point ; and this water becomes the fii-st nom-ish-’
ment of the plant m early spring. The expansion of water during its congelation at
wluch time Its volume mcreascs one-twelfth, and its contraction of bidk dui-frg a thaw
“ ft“ ft"ft“ ft‘“ft" ‘ft
ChiVp . IV.
O f ihe Agency o f ihe Atmosphere in Vegetation.
nhZLil ""'"ft*“ the earth may be studied chemically and
L d pft f fr" elements of which the atmosplicre is composed:
f01 ithhofse e ophfen om’ enfta" 'w" !lu -chT con"s t¥it"u‘tfet ftt®h e weather. and as influenced by viu-ious causes,
iß hi;.,-I
: I-!
ßßf ßt a
I
' f f l i ,
t a l i