1838] 



FARMERS' REGISTER, 



137 



If we follow the two classes through their more 

 roni|iouiHicoiislitueiits, we will firul the aiialoixy still 

 holds: tliey contain cotiinion snirar, mucus, jelly, 

 coloriuiX, and oilier pruiciples, irhiten.* (ihrin. oils, 

 resins, and extractives. The functions of animals 

 and |)lants are similarly closely analojrous. 



Animals take in their tiiod by the agency of the 

 mouth, and prepare it for diijestion by various de- 

 grees of mastication, or atiriiion, as in the pi/.zard 

 of birds. In this they ditierfrom plants, but these 

 have this compensation, they imbibe their food in 

 a liquid form, and consequently in a state of the 

 finest possible division. Animal and vegetable 

 remains are their common food, plants havino; 

 this superiority over animals, that, as they only 

 absorb the soluble and finer parts, they are not 

 obliged to throw off the grosser constituents which 

 appear in the excrement ol"animals.t In the ani- 

 mal stomach the food undergoes an extensive 

 change, being reduced to a pulp of greaterspecific 

 gravity, and being altered entirely both in taste 

 and smell. In the lym|)hatics of plants, which 

 may be considered their primary organ of diges- 

 tion, their food, or lymph, undergoes a chanire 

 precisely similar; its color and flavor are altered, 

 and its specific gravity increased. 



From the stomach, the animafs food passes in- 

 to the intestines, is there subjected to the action of 

 the biie, and converted into chyle, the nutritive 

 part, and excrementiiious matter. In their pas- 

 sage through the intestines, the chyle is absorbed 

 by the lacteal vessels, and is conveyed into the 

 blood; by the heart, the minfrled fluids are pro- 

 pelled into the lungs, to be there exposed to the 

 action of the air. The vital fiuid there changes 

 its purple hue for a florid red, loses a portion of its 

 watery particles and carbon ; the latter combining 

 with the oxygen of the atmospheric air in the 

 lungs, and being breathed forth in the form of 

 carbonic acid gas. As planrs in their food take in 

 no gross, unnecessary ingredients, it is obvious 

 that no process like the biliary operation of diires- 

 tion is required. The lymph, or sap, proceeding 

 at once along the branches, is poured into the 

 leaves, the very lunsfs of plants. There, as in the 

 blood, its color is chanired, oxygen is emitted from 

 it durincT the light hours of the day; but carbonic 

 acid gas is thrown off during the night, and at all 

 periods a considerable quantity of water. 



From the lungs, by the atiency of the heart, 

 »he blood is propelled throufrh the arteries over 

 the whole animal system, supplying nourishment 

 and warmth to all the parts, and where, by these 

 abstractions, it is again converted into purple or 

 venous blood, it is returned by the veins to under- 

 go the chantjes that were described as being ef- 

 fected by the lungs. 



The sap, after exposure to the action of the air 

 in the leaves, is returned by another set of vessels 

 situated in the bark, ministering to the growth 

 and support of the whole plant. 



Such is the close assimilarity in the digestive 

 and circulatory processes of the two classes; an as- 

 similarity which obtains in all the other functions 

 enjoyed by them in common. In respiration, the 



* The gluten of plants is the albumen of animals. 



t Is not the excretion from the roots of plants, as 

 proved to exist by M. De Candolle, somewhat analo- 

 gous to the excrementitious matter of animals? — Edx- 



TOR. 



Vol. VI-18 



air inhaled through the mouth and nostrils pro- 

 ceeds immediately to the lungs and acts upon the 

 blood; in plants, when it is iiilialed by their leaves, 

 it operates instantaneously upon the sap. The 

 changes that take place have just V)ecn imperfect- 

 ly noticed; but it is necessary to add, that the oxy- 

 gen of the atmosphere, is the gas essential to the 

 existence of animals; but it is its carbonic acid 

 that is nearly as imporiant to vegetables. They 

 may be considered the vital airs of the two classes. 

 If animals are placed in a situation where they in- 

 hale pure oxygen, their functions are highly and 

 rapidly increased; but it is an exhilaration which 

 would sQon terminate in exhaustion and death, if 

 breathed by them for any extended period. So 

 plants will flourish in an atmospliere containing 

 yVth of carbonic acid, but if it much exceeds this 

 pi-oportion, they are rapidly destroyed. During 

 sleep, animals expire less carbonic acid than dur- 

 ino their waking hours; so plants emit little or no 

 oxyiren during the night. 



After an animal has enjoyed the regular course 

 of its functions for a period varying in its duration, 

 the time at length arrives when decay commences. 

 The wasted, enfeebled, and relaxed form gradual- 

 ly declines, until death finally closes all activity. 

 The body then becomes contracted and rigid; the 

 skin exchanges the ruddy tinge of health for 

 death's pallid hue. Decomposition speedily en- 

 sues, with all its offensive phenomena; and finally 

 the only permanent remains are the skeleton and 

 asmall amount of earthy matter. Thesame cha- 

 racteristics attend the last period of vegetable ex- 

 istence. Plants may flourish only lor one season, 

 or their lives may be extended through centuries 

 of years, yet decay eventually comes over them; 

 becoming more and more stunted, weak, pallid, 

 and ragged, they eventuall}' cease to live, become 

 contracted and rigid, and pass through the same 

 phases of putrelaction that are exhibited by the 

 animal carcass. In both there was a time when 

 warmth and exposure to the atmosphere were the 

 sources of vigor, they now become the agents of 

 destruction; they were once able to resist and to 

 overcome the laws of chemical affinity, they now 

 are destroyed by their attacks. What causes this 

 most striking change? What antiseptic agent 

 have they lost? There can be but one reply. It 

 was their vitality. Now, let us examine how the 

 vitality of plants in other respects resembles the 

 vitality of animals, and I will confine this exami- 

 nation to two or three points. 



Plants are excitable. Light acts upon them as 

 a stimulus. Every body must have observed 

 that plants bend towards the direction from 

 whence its brightest influence proceeds. M . Bon- 

 net, the French botanist, demonstrated this in 

 some very satisfactory experiments, by which he 

 showed that plants grown in a dark cellar, all ex- 

 tended themselves towards a small orifice admit- 

 ting a few rays of light. Every flower almost 

 has a particular degree of light requisite for its lull 

 expansion. The blossoms of the pea, and of other 

 pajjilionaceous plants, spread out their wings in 

 fine weather, to admit the solar rays, and again 

 close them at the approach of night. Plants re- 

 quiring a powerful stimulus, do not expand their 

 flowers until noon, whilst some would be destroy- 

 ed if compelled to open in the meridian sun, — the 

 night-blooming Cereus unfolds its flowers only at 

 night. Heat also acts as a stimulus upon plants. 



