SCIENTIFIC HISTORY OF A PLANT. 



benefits he has conferred upon science are very great, for this reason : they are twofold 

 in their nature. Besides the actual results of his own labors — 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, in the end he would benefit science. The past histor}' of inductive science con- 

 firms this statement. We cannot now afford time to trace the origin and rise of agricultu- 

 ral 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 are various actions alwa}'S going on in a plant, owing to the decomposition 

 of certain 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 very often con- 

 founded with each other. I refer to the decomposition of carbonic acid and of water — to 

 the absorption of oxygen during darkness — 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 absorbtion of oxj'gen during the night is entirel}'^ a chemical process; 

 the emission of carbonic acid being, on the other hand, a purely mechanical operation. 



For the decomposition of carbonic acid and water, we find that light is required; that 

 where there is a deficiency of light this action goes on put partially. Researches have 

 proved that 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 germination to be entirely dependent upon the actinic, but to be act- 

 ually impeded by the luminous rays; while on the other hand, this decomposition of car- 

 bonic 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 pa- 

 rathermic rays are most conducive both to fruiting and flowering. All that we can say to 

 these carefully investigated and well proved facts, is, that the}'^ give us one of the most 

 striking examples of the adaption 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 ab- 

 sorbed, but not alwaj's, as I have before mentioned, being decomposed; for in the dark 

 this action is 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 Lie- 

 big — this emission of water and carbonic acid from a plant in the dark — " to a cotton wick 

 enclos-ed in a lamp containing a liquid saturated with carbonic acid." Water and carbon- 

 ic acid are taken up by 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 evolution of carbonic acid was purely me- 

 chanical. Yet, because they occur simultaneously, it was presumed that they were sub- 

 ject to the like causes; even after it was found that their ratios of action were not equal; 

 for plants absorb more oxj'gen than they emit carbonic acid. 



This nightl}' absorbtion of carbonic acid is, to a certain extent, independent of the life 

 of the plant, not acting upon the main parts, but upon the blossoms, fruit and leaves, and 

 the result of experiment has revealed to us the facts, that leaves containing highly nitro 

 genised compounds, or volatile oils, absorb oxygen more vigorously than leaves which 

 tain neither of these principles. In the latter class of leaves the volatile oil, by the 



