1839] 



i^' A R Al E R S = R E G i S T E R 



m 



Should it be objected, that although the texture 

 of these vessels is such as to fit them for such a 

 work, yet we can conceive of no way in which the 

 vital principle, be that principle what it may, can 

 operate so as to produce this ctFect. In answer, 1 

 would say, neither can we conceive o(" the way in 

 which the vital principle operates to produce sim- 

 ilar dilatauons in the heart of man ; and yet we 

 know from actual observation that such etiects are 

 produced. These notions take place as long as 

 the man remains alive ; the moment he dies, they 

 cease at once; hence we ascribe ihem to the imme- 

 diate agency of the vital principle ; and although 

 the way in which v/hat we have termed the vital 

 principle produces this effect is an inexplicable 

 mystery, and in all probability will ever remain 

 such, yet we never think of calling the fiact that 

 such motions do take place, in question, on that 

 account. 



But it may be further objected, that these mo- 

 tions in animals appear to be inseparably connec- 

 ted with a nervous system ; and that no such 

 system exists in vegetables. This remark is not 

 strictly true. "The nervous system, which is very 

 distinct from all others in animals of the higher 

 classes, gradually tends to divide; and finally, one 

 is forced to admit, that in zoophytes the nervous 

 matter is diffused, as it were, throughout the whole 

 body, so that they possess a kind of universal sen- 

 sibility, without there being any where a nervous 

 system distinct from the ti^suer?." If such is as- 

 certained to be the fact with respect to zoophytes, 

 why may we not go a step further; and suppose 

 that in vegetables the nervous matter is unilbrmly 

 diffused, or, what amounts to the same thing, and 

 will perhaps appear less objectionable, that (he 

 tissues are constructed in such a way as to be ca- 

 pable of performing so many of the lijncticns of a 

 nervous system, as are necessary in the economy 

 of vegetable life. There is no essential difference 

 in the composition of the most perfect nervous 

 system, ancl the other parts of the animal body, 

 which would forbid such a supposition. They 

 are all composed of the same elements, and differ 

 only in the manner in which those elements are 

 organized. The fact, that when certain poisons 

 are made to enter vegetable systems, or when 

 plants are killed by electricity, the tissues at once 

 stiflfen and become entirely incapable of circulating 

 the sap, favors this idea. But whatever expla- 

 nation we may give of the matter, the facts of the 

 case seem to require, that we admit the existence 

 of alternate dilatations and contractions in the tis- 

 sues of plants, produced immediately by the vital 

 principle. 



Chapter XVI. 



FOOD OF PLANTS. WATER. CARBOKIC ACID 

 GAS. NITROGEN. OTHER SUBSTANCES FOUND 

 IN PLANTS. 



In speaking of the composition of vegetable sub- 

 stances, chemists distinguish between their prox- 

 imate and ultimate principles. The ultimate prin- 

 ciples of vegetables, are the simple elementary 

 substances of which they are composed, such as 

 carbon, oxygen, &c. The proximate principles, 

 are those compounds into which these elements 



are united by the action of vegetable systems, such 

 as, gum, resin, sugar, &c. 'i'he ultimate elements 

 of which all vegetable substances are composed, 

 are but Itiw. Carbon, oxygen and hydrogen, are 

 the only ones which exist in any considerable 

 quantity, and where others enter, they seem to 

 enter rather as accidental, than as essential inore- 

 dicnts. The proximate principles are very nume- 

 rous, and every year, t lie researches ol"the chemist 

 are adding to their number; yet a> they are all made 

 up of pretty much the same ultimate elements, 

 ihey must of. course, resemble each other closely 

 in comparison. In order that a plant may increase 

 in size, it must be supplied with carbon, oxygen 

 and hydrogen, which may be considered the raw 

 materials of the vegetable fabric, and of course 

 the food of plants must contain these elements, 

 either in a separate state, or in such compounds as 

 the organs of the plant shall be able to decom- 

 pose. 



It was at one time believed that pure water wag 

 capable of sustaining and nourishing plants, and 

 that in fact it was their only proper (ood. This 

 opinion was founded in part upon such experi- 

 ments as the following of Von Helmont. Hav- 

 ving placed a young willow in a box containing 

 a known quantity of pure sand, and supplied it 

 plentifully with water, it was found to increase in 

 size very rapidly. Alter being suffered to grow 

 for a time, it was removed, and the sand carefully 

 weighed; when it was found to have undergone 

 no perceptible variation in weight. Hence, it was 

 inferred that the plant was nourished by the wa- 

 ter alone. It was afierwards su^zgested to this 

 experimenter, that in as much as he used com- 

 mon spring water, tliat water n)ight contain other 

 substances in solution. He repeated the expe- 

 riment, using distilled in the place of common 

 water, and the plant died. But without the de- 

 cisive result of tlie last experiment, we might be 

 satisfied that the opinion was erroneous, from our 

 knowledge of the composition of water. Water 

 consists of oxygen, and hydrogen, and nothing 

 else. Now, if pure water is the only proper food 

 for plants, whence is it that they are to obtain their 

 carbon, an element which enters largely into the 

 composition of every part ol" the vegetable struc- 

 ture. 



The fact seems to be, that what may properly 

 be called the food of plants, because it is that 

 without which they cannot exist, is atmospheric 

 air, to<;e!her with water, containing carbonic acid 

 gas in solution; and these alone are sufTicient for 

 their support. Water has the power of absorbing 

 and retaining a large portion of many of the 

 .'rases; of carbonic acid gas, recently boiled water 

 vviil absorb its own volume. Placed as water in 

 ordinary cicumstances is, in contact with the at- 

 mosphere, which always contains a greater or less 

 portion of carbonic acid gas diffused throughout it, 

 it v.'ill always, when subjected to examination, be 

 ftund to contain a portion of this' gas in solution. 

 It is probably in this way that the greater part of 

 the carbon which exists in vegetables, is intro- 

 duced. This carbonic acid is derived from many 

 sources; but principally from the decomposition of 

 the various organic substances which lie buried in 

 the soil, or scattered upon its surface. All vege- 

 tables, when they rot, or undergo decomposition, 

 are resolved principally into water, carburetted-hy- 

 drogen and carbonic acid ; and it is to their ability 



