424 



F A R M E R S • li E G I S T iC 11 , 



[No. 7 



to supply this last mentioned substance, tliiit pu- 

 trescent manures owe tlieir nutrilive properlios. II' 

 we look at the effects ol' such manures, we will 

 find that their enerrfy is proportioned to their ca- 

 pability of Ibrming this acid. "Yeast, for in- 

 stance, wliich is one of the most active of these 

 manures, is so from possessin<}:, beyond all other 

 substances, the power of exciting lijrmentation, 

 and thus of causinf; the Ibrmalion of carbonic 

 acid from the vegetable matter which lies buried in 

 the soil." 



It is only in the state of carbonic acid that car- 

 bon can enter into the system of a plant. If a 

 plant is placed in solid carbon, and watered with 

 distilled water, it might as well be planted in pow- 

 dered glass, so far as its growth is concerned. Sir 

 H. Davy placed a plant of mint in water mixed 

 with carbon in a state of impalpable powder, and 

 he found that not a particle could enter the roots. 

 Wlien carbonic acid enters the system of a plant, 

 it suffers decomposition, its oxygen being liberated 

 and its carbon fixed in the tissues. This has been 

 proved by many very satisfactory experiments. If 

 fresh gathered leaves be placed in water, and 

 thus situated, be exposed to direct sunlight, they 

 will soon be covered with minute air bubbles, 

 which if collected and examined, will be found to 

 be pure oxygen. The earliest observers of this 

 circumstance supposed these bubbles to be libe- 

 rated from the water by ihe heat of the sun ; for 

 when leaves were placed in water Vv'hich had been 

 deprived of the air which it contained by boiling, 

 no bubbles appeared. The correct explanation of 

 this fact is, that in such circumstances, there is no 

 carbonic acid furnished by the water for tlie plant 

 to decompose. 



De Candolle has proved that the oxygen we col- 

 lect in such cases, arises fi-om the decomposition of 

 carbonic acid in the following manner. He placed 

 in a pneumatic cistern filled with distilled water, 

 two inverted glass jars: one of which was filled 

 with the water of the cistern, and had floating in 

 it a plant of mint; ^h'^. other contained carbonic 

 acid gas. To prevent all absorption of carbonic 

 acid from the atmosphere, the surface of the water 

 in the cistern was covered with a thick layer of 

 oil. The whole apparatus thus arranged was ex- 

 posed to direct sun-fight. The carbonic acid soon 

 began to disappear, but just as fast as it disap- 

 peared from one vessel oxygen appeared in the 

 other. In order to understand this experiment it 

 is necessary to bear in mind the fact, that the ele- 

 ments of carbonic acid are condensed into one-half 

 tlieir original volume when they combine with 

 each other. If 100 cubic inches of oxygen unite 

 with 100 cubic inches of the vapor of carbon, they 

 will not form 200 cubic inches of the resultinir com- 

 pound, but each being condensed into one-hnif its 

 original volume, they will form but 100 cubic 

 indies. Just the reverse ol' this takes place when 

 carbonic acid is decomposed ; every 100 cubic 

 inches of carbonic acid will furnisli 100 cubic in- 

 ches of oxygen, and 100 cubic inches of the vapor 

 of carbon. This explains the fact that oxygen 

 appeared in one bell glass just as fast as carbonic 

 acid disappeared from the other. He afterwards 

 varied the experiment by substituting oxygen for 

 the carbonic acid in the second glass. In this case 

 no gas was given off by the plant, neither did any 

 of the oxygen disappear ; thus proving that plants 

 have a specific power of absorbing carbonic acid, 



and aficr decomposing it, of retaining the carbon 

 and rejecting the oxygen; and iliat the oxyen 

 given off l>y growing plants is derived from the 

 decomposition of carbonic acid. 



Two conditions appear to l)e necessary for the 

 successful repeiilion of this experim.ent. 1st. That 

 the plant should be green and living, since it has 

 been found that recently killed, but si ill green 

 plants, emit no gas. 2nd. Exposure to direct sun- 

 liiiht, for neither the clear light of day, nor that of 

 the brightest lamp produce any effect. l''wn) some 

 experiments recently perlhrmed, it would seem 

 that this cficct is due entirely to the chemical part 

 of the ray of light. It has long been known that 

 a ray of solar light was composed oi' three dis- 

 tinct and separable rays, viz, a luminous ray; a 

 heating, or as it is more commonly called, a calo- 

 rific ray, which is not luminous ; and a chemical 

 ray which is neiiher heating nor luminous. By a 

 certain contrivance, it is easy to absorb any two of 

 these rays, whilst the third is suffered to pass on 

 undisturbed. By subjecting a plant to each of the 

 three raj's in succession, it has been found that it 

 is the chemical ray alone which is capable of pro- 

 ducing any effect. These facts should be borne in 

 mind by any one who maj- wish to repeat the ex- 

 periments of De Candolle. 



Although all experiments combine to prove that 

 carbonic acid is the most essential of ihe elemenis 

 on which plants are nourished : yet water is also 

 a necessary part of their food. It is true that a 

 large portion of the water taken up by a plant is 

 lost again by evaporation, yet accurate experi- 

 ments show that a portion of it actually enters into 

 ihe composition of the plant. Saussure found that 

 when plants were grown in close vessels, in an at- 

 mosphere containing a little carbonic acid, the 

 weight which the plant acquired in a given time, 

 was much greater than that of the carbon pro- 

 duced by the decomposition of carbonic acid, and 

 this could be accounted for in no other way than 

 b}' supposing it to liave fixed a considerable quan- 

 tity of water ; thus plants of the vivcn, which in 

 a vessel without carbonic acid had gained \'^ grains 

 from water only ; acquired 5 -^\- grains when they 

 were at the same time able to procure carbonic 

 acid. That water is an essential part of the food 

 of plants, may be learned from (he iiict, that almost 

 all the proximate principles contain hydrogen, an 

 element which does not exist in carbonic acid, and 

 of course cannot be flirnished by it. The water 

 which enters inio the composition of a plant, pro- 

 bably enters without undergoing decomposition. 

 On this subject Prof. Lindley remarks, "as it has 

 been pretty well made out that all the oxygen 

 given off l>y plants, is produced by the decompo- 

 siiion of carbonic acid, and as no one has ever 

 been able to detect the emission of hydrogen by 

 any plant except mushrooms, it is inferred that if 

 flie water which is consumed by plants is ever de- 

 composed, it is in Ihe form.ation of the various 

 proximate principles which contain more oxygen 

 (viz. acids,) or more hydrofjen (viz:, oil?^,) llian 

 water; but as the greater part of vegetable sub- 

 stances, such as gum, sugar, fecula, &c., contain 

 oxygen and hydron;en in the same proportion as 

 water, it can hardly be doubted that the water un- 

 dergoes no decomposition, but is simply fixed."' 



"It was formerly thought that nitrogen or axote 

 had nothing to do with the nourishment of plants; 

 and that, in those cases where it was met with, it 



