ASSIMILATION OF CARBON. 



21 



form of a spongy mass, the minute pores of 

 which can be seen only by a microscope. 



Chemistry offers innumerable resources 

 of this kind which are of the greatest use in 

 an inquiry into the nature of the organs of 

 plants; but they are not used, because the 

 need of them is not felt. The most import- 

 ant organs of animals and their functions 

 are known, although they may not be visi- 

 ble to the naked eye. But in vegetable phy- 

 sioijgy, a leaf is in every case regarded 

 merely as a leaf, notwithstanding that leaves 

 generating oil of turpentine or oil of lemons 

 must possess a different nature from those 

 in which oxalic acid is formed. Vitality, in 

 its peculiar operations, makes use of a spe- 

 cial apparatus for each function of an organ. 

 A rose twig engrafted upon a lemon tree 

 does not bring forth lemons, but roses. 

 Vegetable physiologists in the study of their 

 science have not directed their attention to 

 that part of it which is most worthy of in- 

 vestigation. 



The second cause of the incredulity with 

 which physiologists view the theory of the 

 nutrition of plants by the carbonic acid of 

 the atmosphere as, that the art of experi- 

 menting is not known in physiology, it being 

 an art which can be learned accurately only 

 n the chemical laboratory. Nature speaks 

 "ft us in a peculiar language, in the language 

 of phenomena; she answers at all times the 

 questions which are put to her; and such 

 questions are experiments. An experiment 

 is the expression of a thought : we are near 

 the truth when the phenomena elicited by 

 the experiment corresponds to the thought; 

 while the opposite result shows that the 

 question was falsely stated, and that the 

 conception was erroneous. 



The critical repetition of another's experi- 

 ments must be viewed as a criticism of his 

 opinions ; if the result of the criticism be 

 merely negative, if it do not suggest more 

 correct ideas in the place of those which it 

 is intended to refute, it should be disre- 

 garded ; because the worse experimenter the 

 critic is, the greater will be the discrepancy 

 between the results he obtains and the views 

 proposed by the other. 



It is too much forgotten by physiologists, 

 that their duty really is not to refute the ex- 

 periments of others, nor to show that they 

 are erroneous, but to discover truth, and 

 that alone. It is startling, when we reflect 

 that all the time and energy of a multitude 

 of persons of genius, talent, and knowledge, 

 are expended in endeavours to demonstrate 

 each other's errors. 



The question whether carbonic acid is the 

 food of plants or not has been made the sub- 

 ject of experiments with perfect zeal and 

 good faith ; the results have been opposed 

 to that view. But how was tne inquiry in- 

 stituted'? 



The seeds of balsamines, beans, cresses, 

 and gourds, were sown in pure Carrara 

 marble, and sprinkled with water containing 

 carbonic acid. The seeds sprang, but the 



plants did not attain to the development of 

 the third small leaf. In other cases, they 

 allowed the water to penetrate the marble 

 from below, yet, in spite of this, they died. 

 It is worthy of observation, that they lived 

 longer with pure distilled water than with 

 that impregnated with carbonic acid; but 

 still, in this case also, they eventually pe- 

 rished. Other experimenters sowed seeds 

 of plants in flowers of sulphur and sulphate 

 of barytes, and tried to nourish them with 

 carbonic acid, but without success. 



Such experiments have been considered 

 as positive proofs, that carbonic acid will 

 not nourish plants ; but the manner in which 

 they were instituted is opposed to all rules 

 of philosophical inquiry, and to all the laws 

 of chemistry. 



Many conditions are necessary for the 

 life of plants ; those of each genus require 

 special conditions ; and should but one of 

 these be wanting, although the rest be sup- 

 plied, the plants will not be brought to ma- 

 turity. The organs of a plant, as well as 

 those of an animal, contain substances of 

 the most different kinds; some are formed 

 solely of carbon and the elements of water, 

 others contain nitrogen, and in all plants we 

 find metallic oxides in the state of salts. 

 The food which can serve for the produc- 

 tion of all the organs of a plant, must neces- 

 sarily contain all its elements. These most 

 essential of all the chemical qualities of nu- 

 triment may be united in one substance, or 

 they may exist separately in several ; in 

 which case, the one contains what is want- 

 ing in the other. Dogs die although fed 

 with jelly, a substance which contains ni- 

 trogen ; they cannot live upon white bread, 

 sugar or starch, if these are given as food, 

 to the exclusion of all other substances. 

 Can it be concluded from this, that these 

 substances contain no elements suited for 

 assimilation? Certainly not. 



Vitality is the power which each organ 

 possesses of constantly reproducing itself ; 

 for this it requires a supply of substance a 

 which contain the constituent elements 

 of its own substance, and are capable 

 of undergoing transformation. All the 

 organs together cannot generate a single 

 element, carbon, nitrogen, or a metallic 

 oxide. 



When the quantity of the food is too 

 great, or is not capable of undergoing the 

 necessary transformation, or exerts any pe- 

 culiar cnemical action, the organ itself is 

 subjected to a change : all poisons act in this 

 manner. The most nutritious substances 

 may cause death. In experiments such as 

 those described above, every condition of 

 nutrition should be considered. Besides 

 those matters whi"h form their principal 

 constituent parts, both animals and plants 

 require others, the peculiar functions ot 

 which are unknown. These are inorganic 

 substances, such as common salt, the total 

 want of which is in animals inevitably pro- 

 ductive of death. Plants, for me same rea- 



