SCIENTIFIC HISTORY OF A PLANT. 



of oxygen, is converted into a resin. The Agave americana, absorbs 0.3 times its volume 

 of oxj'gen in twenty-four hours; the Pinus abies, containing volatile and resinous oils, 

 ten times its volume of ox\'gen in the same time; the Quercus robur, containing tannic 

 acid, fourteen times its volume of oxygen; and the Populus alba, twenty-one times its vo- 

 lume of oxj'gen during a day and night. 



I need hardly mention as a familiar example of these chemical changes, caused by the 

 absorption of oxygen, Cacalia ficoides, which is sour in the morning, tasteless at noon, 

 and bitter in the evening from the excess of hydrogen; it became tasteless when there was 

 no excess of oxygen, and sour owingto the oxygen which it had absorbed duiingthe night. 



This decomposition of carbonic acid is most interesting to us as exhibiting clearly the 

 real process of lignification; as helping to establish correct notions regarding that vegeta- 

 ble matter undergoing eremacausis which is familiarly known as humus; experiments have 

 proved the insolubility of humus; calculations have demonstrated, that suppo.se there ex- 

 isted a superabundance of the most soluble salt of humic acid, still all the carbon which 

 it might contain, would be totally inadequate to give us but a very small portion of that 

 carbon which is found in vegetation. But another calculation was made as to a different 

 source for the carbonic acid; a calculation which was based upon De Saussure's accurate 

 determination of the amount of carbonic acid present in the atmosphere, an amount of a 

 little more than one-thousandth of its weight; yet we find that the air contains no less 

 sum than 3085 billions of pounds of carbon, a quantity surpassing in weight not only the 

 carbon of existing vegetation, but also that which is at present locked up in the mineral 

 coal which is distributed over certain parts of the earth's sui'face. 



It may now well be asked. How lives the3'oung plant before it comes in contact with the 

 atmosphere, the source of its carbonic acid? The rei)ly to this question is the ke^^ to the 

 proper action action of humus. This humus is especially useful for the support of young 

 plants; it takes oxygen from the air; and then furnishes the plant with caibonic acid 

 — tliis is its great use. We see, then, that the process of nouiishmentin a young plant 

 totally differs from those actions by which the well developed vegetable is supported. A 

 j^ouiig plant causes a certain quantity of oxj'gen to be abstracted from the atmosjihere, 

 while an old one furnishes us M'ith a never-failing source of this gas. 



I cannot help referring to the fact, that many juicy and milky plants in warm countries, 

 flourish on ^ soil destitute of humus, containing absolutely not a trace of carbon; and 

 sometimes are found being held by one point of attachment to this barren soil — such shrubs 

 as the Cactus and the Caoutchouc are among this number. Baron Humboldt especially 

 mentions the Cactus tribe. In his beautiful paper on the " Physiognoniy of Plants," he 

 states: — " In the waterless plains of South America, animals suffering from thirst seek 

 the Mdon- Cactus, a spherical plant half buried in the dry sand, and encased in foimida- 

 ble prickles, but of which the interior aboynds in refreshing juice. The stems of the co- 

 lumnar Cactus often rise to the height of fioin thirty to thirty-two feet; they are often 

 covered with lichens, and dividing into candelabra-like handles, resemble in physiognomy 

 some of the Euphorbias of Africa." Again, in note 20: — " AVhen one has been accustom- 

 ed to see Cactuses only in our hot-houses, one is astonished at the degree of density and 

 hardness which the ligneous fibres attain in old Cactus stems. The Indians know the 

 Cactus wood is incorruptible and excellent for bars and the thresholds of doors. Tliere 

 is hardly anytl),ing in vegetable physiognomy that makes so iiregular and ineffaceable an 

 impression upoji a newly arrived person, as the sight of an arid plain thickly covered 

 o!-e near Cumar^a, New Barcelona and Cora, with columnar and candelabra-1 

 Cactus stems.'* 



