THE SCIENTIFIC HISTORY OF A PLANT. 
fold in their nature. Besides the actual results of his own labours — and they are many and various 
he opened a new field for the direction of the energies of other men. Were his theories all wrong — 
his researches all false — still, if by them the spirit of inquiry was aroused, hi the end he would benefit 
science. The past history of inductive science confirms this statement. We cannot now afford 
time to trace the origin and rise of agricultural chemistry, but must be content with a slight glance at 
it as it now exists — a product of the mental exertions of the German professor. 
The first point of importance upon looking at the chemical phenomena of vegetation, is, that there 
The chemical ana piiy- ar e various actions always going on in a plant owing to the decomposition of certain 
sicai actions of a plant, portions of its structure, or of the materials whence it derives its food — actions 
extremely different to those mechanical actions to which I have before alluded. They are changes 
which at first sight appear to be strictly chemical, and which are veiy often confounded with each other. 
I refer to the decomposition of carbonic acid and of water — to the absorption of oxygen during dark- 
ness — to the emission of carbonic acid during the night. The decomposition of carbonic acid and of 
water may be designated as chemico-physical action ; the absorption of oxygen during the night is 
entirely a chemical process ; the emission of carbonic acid being, on the other hand, a purely mechani- 
cal operation. 
For the decomposition of carbonic acid and water, we find that light is required ; that where there 
Action of light npon is a deficiency of light this action goes on but partially. Researches have proved that 
vegetation. while the blue rays are most active in germination, the yellow rays act more readily 
on the developed plant. Mr. Robert Hunt, in a lecture which he delivered at the Royal Institution 
last year, on " Light and Actinism," stated some valuable and curious facts. He considers germina- 
Mr. Robert Hunt on tion to be entirely dependent upon the actinic, but to be actually impeded by the 
actinism ana vegetation, luminous, rays ; while, on the other hand, this decomposition of carbonic acid, this 
lignification is most extensively carried on by the action of the luminous power, and is stopped by the 
actinic force. As summer advances, the thermic and the paratherrnic rays are most conducive both to 
fruiting and flowering. All that we can say to these carefully investigated and well proved facts, is, 
that they give us one of the most striking examples of the adaptation of inorganic nature to organic 
life that can be found in the whole range of physical science. 
From the first moment of the germination of a seed, carbonic acid is always being absorbed, but not 
Ni»huy absorption and a h>vays, as I have before mentioned, being decomposed; for in the dark this action is 
emission of carbonic stopped, but the carbonic acid still continues to be absorbed by the juices which the 
plant holds in solution. This action was very aptly compared by Professor Liebig — 
this emission of water and carbonic acid from a plant in the dark — " to a cotton wick enclosed in a 
lamp containing a liquid saturated with carbonic acid." Water and carbonic acid are taken up the 
wick by capillary attraction, both evaporating on its exterior surface. In the night another action 
goes on in the growth of plants — the absorption of oxygen ; an action as purely chemical, as the evolu- 
tion of carbonic acid was purely mechanical. Yet, because they occur simultaneously, it was presumed 
that they were subject to the like causes ; even after it was found out that then- ratios of action were not 
equal ; for plants absorb more oxygen than they emit carbonic acid. 
This nightly absorption of carbonic acid is, to a certain extent, independent of the life of the plant, 
various results of the no ^ act ^ n o u P on the main parts, but upon the blossoms, fruit, and leaves, and the 
nightly absorption of result of experiment has revealed to us the facts, that leaves containing highly 
nitrogenised compounds, or volatile oils, absorb oxygen more vigorously than leaves 
which contain neither of these principles. In the latter class of leaves the volatile oil, by the action 
of oxygen, is converted into a resin. The Agave americaua, absorbs 3 times its volume of 
oxygen in twenty-four hours ; the Pinus Abies, containing volatile and resinous oils, ten times its 
volume of oxygen in the same time; the Quercus Robur, containing tannic acid., fourteen times its 
volume of oxygen ; and the Populus alba, twenty-one times its volume of oxygen during a day 
and a night. 
I need hardly mention as a familial' example of these chemical changes, caused by the absorption of 
Cacaiia neoides. oxygen, the Cacalia ficoides, which is sour in the morning, tasteless at noon, and bitter 
in the evening froni the excess of hydrogen ; it became tasteless when there was no excess of oxygen, 
and sour owing to the oxygen which it had absorbed during the night. 
This decomposition of carbonic acid is most interesting to us as exhibiting clearly the real process 
correct theory of bu- °f lignification ; as helping to establish correct notions regarding that vegetable 
mus - matter undergoing eremacausis which is familiary known as humus; experiments 
have proved the insolubility of humus ; calculations have demonstrated, that suppose there existed a 
superabundance of the most soluble salt of humic acid, still all the carbon which it might contain, 
<73 g^g y<^ g 
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