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many uncertain points of opinion to be settled before our perceptions of it can be complete and satisfactory.

Son. Your praise of the science of botany may be very true, but I fancy that there is some slight contradiction, or at least it appears ambiguous to me, that if it is distinguished for the correctness and clearness of its reasonings, there should still appear many uncertain points of opinion to be settled before our perceptions of it can be complete and satisfactory. Mr. B. I am glad that your perception is so quick, and can only account for the discrepancy by informing you that the science of botany is divided into four grand divisions: first, Descriptive Botany, from which we learn the art of describing plants with accuracy, so that their characters may be recognised with certainty by others, and of giving to plants names by which they can be mentioned without confusion when written or spoken of. Second, Systematic Botany, which explains the principles upon which are determined the mutual relations that combine the seemingly discordant members of the vegetable kingdom into one harmonious whole, and which teaches the art of distinguishing any plant from all others, so as always to determine its name with precision.

Now these two divisions compose the parts of botany distinguished for the correctness and closeness of its reasonings; and the two following contain the uncertain points of opinion to be settled by further investigation, before our perception of them can be complete and satisfactory: viz., Structural Botany, which comprehends whatever relates to the laws of vegetable structure, whether external or internal, independently of the presence of a vital principle; and Physiological Botany, to which belongs all that concerns the history of vegetable life, from the moment when the vital principle is imparted to the seed, and the plant first breaks its shell, to the period of death; explaining the functions which the various organs are destined to perform, the changes they undergo in health and sickness, and under the influences exercised by climate, seasons, accidents, or the act of man.

I mean in these lessons to confine myself to the Descriptive department of the science, or that part devoted to the examination, description, and classification of all the circumstances connected with the external configuration and internal structure of plants; which, in the words of Professor Henslow, we may here consider in much the same light as so many pieces of machinery, more or less complicated in their structure, but of whose several parts we must first obtain some general knowledge before we can expect to understand their modes of operation, or to appreciate the ends which each was intended to effect.

In the "Physiological," which is the other department (of which I mean to treat in a separate course of lessons), we consider these machines, as it were, in action.

Vegetable Physiology.

Mr. B. It is to the physiology of vegetables, practically considered, that I purpose to direct your attention this evening. The physiology of the vegetable kingdom is a science full of interest, of great practical utility, more especially to the gardener, but also to the dyer, the weaver, the chemist, who all turn it to account; and, indeed, scarce an art exists, on which it does not confer some benefit. The study of the subject tends to rivet the attention, to interest the human mind, and to lead man with admiring wonder to the contemplation of the beneficent Being who formed the objects which it embraces, causing them to stand as the connecting link between the animal and the mineral creation; receiving from the one what is indispensable to the wellbeing and enjoyment of the other.

Perhaps the most natural mode of entering upon this subject will be, to note some of the particulars which constitute the difference between the two kingdoms of organised nature. There are points of analogy which extend far between them. Both are capable of reproduction, both prolong their existence and increase their bulk, by receiving within themselves bodies of natures different from their own, which they assimilate to their own substance.

All physiological writers, ancient and modern, seem to be agreed that the causes of life and organisation are utterly invisible, and that whatever they be, they have been operating since the world began, and throughout the world operating regularly without intermission, in various places at the same time. All seem agreed that their modes of operation are strictly methodical, that they seem to act on definite plans, and actually exhibit specific varieties of chemical combination and mechanical structure which human intelligence cannot comprehend. From their mutual dependence, and other relations subsisting between them, all seem to speak as if they were subjected to one great Cause which regulates and harmonises the whole. All seem agreed that wherever the human race has been found, whether civilised, barbarous, or savage, there is a general impression on their minds that

their animating principles, with new bodies, are to exist in a future state, and in that state to be more or less happy according to the deeds of the present life.

In the concise but sublime account as given by the prophet Moses, the law-giver of the Jews, a rational and adequate cause is assigned for the first formation of animals and plants, for their division into different orders, genera, and species; and for the division of some of their species into two sexes. The cause that he assigns, not only for the orderly arrangement of the universe, but for the first formation of the various species of animals and plants, is an omnipotent, omniscient, omnipresent Being-invisible, self-existent, and eternal; and to whose will the whole material universe is subjected, more thoroughly and completely, though not more inconceivable, than our bodily organisms are subjected to our wills. We know that all the organisms of animals and plants are formed out of fluids, and that in a certain species of fluid secreted from the parent, and afterwards enclosed in a very thin and transparent vesicle, there is a living, organising principle, which also acts upon the fluid in a way which we know not, forming out of it a regularly organised system of solids, and forming not only the rudiments of that system, but causing it afterwards to be nourished, and to grow through the medium of fluids, which are moved and distributed under the influence of this organising, animating principle.

Journeyman. I have listened most attentively, and endeavoured to understand all you said, but I must confess that there were some crackjaw words that I could not comprehend.

Mr. B. When these lessons appear in print (as I intend to publish them for the information of young gardeners), you will then be better able to comprehend the meaning of each sentence. When reading, it is advisable, whenever you come to a word that you do not understand, to look for the meaning in a dictionary (which is an indispensable companion). The act of hunting for, and finding the meaning in the dictionary will impress it more forcibly on your mind. To read profitably, it is necessary to fix the attention, to divest yourself of all thoughts foreign to the subject on which you are engaged, and at the end of each page or chapter to take a review of it mentally; that is, to close the book, and to repeat as well as your recollection serves, the words that you have read. When you find yourself deficient in the main particulars, read it again and again, until you make yourself master of it. I recollect calling one evening upon my friend, Mr. John Caie, one of the most philosophic and scientific gardeners

we have. A book, "Representative Men," by Emmerson, was before him. Some weeks after, I called again, and the same book was on the table. I jestingly upbraided him on his slow reading, when he replied, "I have read that book four times, and have only broken the shell, and shall read it again to get at the kernel."

But to return from our digression to the subject in hand. It will be sufficient for our purpose, without entering into more minute particulars, to know that there are male and female organs in animals, destined for reproduction, and that there are similar organs in vegetables. The lungs, or breathing apparatus of animals, are composed of an immense number of cells, which alternately inflate and collapse, as the lungs are filled and emptied of air. When an inspiration is made, and the lungs are filled with air, the cells become expanded, and the blood sent from the right side of the heart, and spread over the cells, is exposed through an extremely thin membrane to the air. An important change here takes place in the blood; from being of a dark purple colour, it immediately changes to a bright scarlet, having absorbed or taken up all the oxygen or vital part of the air, and parted with a corresponding volume of carbonic acid gas, or fixed air, which it had acquired in its circuit through the vessels of the body. So essential is the matter imparted by the air to the blood, for sustaining animal existence, that the breathing cannot be suspended even for a very short period, without extinguishing life. It is considered also probable, that the heat of the body is generated and constantly kept up in some way or other by means of this process of breathing, and the change which the blood undergoes. We know at least, that the evolution of carbonic acid cannot go on, in ordinary chemical processes, without an accompanying discharge of heat; and hence it is presumed that the vital warmth derived from the body may be in this way produced. It was stated by the Rev. A. Huxtable in a public lecture, "that the heat of our bodies is produced in the same way as a room is warmed by the burning of the coal in the grate-the carbon of our food is burned within us as the carbon of the coal is in the grate; and the products in either case are the same. The carbonic acid gas formed in the fire-place goes up the chimney, and the carbonic acid gas formed in our bodies from burning our food is carried forth by our breath, whilst the ashes in the grate correspond to the excrements of man." The functions of respiration, perspiration, and digestion, are performed by the leaves of plants, and the healthiness of a plant is in proportion to the degree in which these functions are duly performed.

Leaves are the laboratory; in them the change of sap, from its crude state into that which it assumes before it is fit to nourish the vegetable, takes place. If you look at a leaf-the horse-chesnut for instance-you will see the dorsal or midrib that divides the leaf from the base to the submit, like the backbone of animals; others branch out from this laterally like the ribs of an animal, which again divide into smaller ones, like the intercostal muscles of animals, all of which terminate on the surface of the leaf by pores, called stomas. These stomas perform three offices: the first, to exhale the superfluous moisture of the plant; the second, to expose the sap which has found its way up to the leaves to the action of the atmosphere, which is requisite in order to effect the chemical change which is necessary before it can descend to nourish the plant; and the third, to attract carbonic acid gas from the common air. Although the portion of carbonic acid gas in the atmosphere is very small (only one gallon in 2500), it is the source from whence plants derive half their dry bulk; hence nature's contrivances to catch, as it fleets by, the minute portion of its food which the air contains. More of that food could not be there without injury to animal life, but as Professor Johnston beautifully expresses it-" To catch this very minute quantity, the tree hangs out thousands of square feet of leaf in perpetual motion through an ever-moving air; and, thus by the conjoined labour of millions of pores, the substance of whole forests of solid wood is slowly extracted from the fleeting winds." The stomas also absorb moisture under certain circumstances, and they both imbibe and give out air; every part of a plant, except its roots, is furnished with stomas, but they are much more abundant upon the leaves than in any other part, and usually abound much more on their under than upon their upper surfaces; excepting in the case of aquatic plants, which are entirely destitute of them on their under surfaces, as they could not evaporate into water, nor receive from it the necessary benefit of exposure to atmospheric air.

Analogous to the stomas of vegetables, are the pores of the human and other animal bodies, and which are the mouths of the exhalent vessels. Physiologists tell us that digestion is not brought about by any mechanical means, as by the grinding powers of the coats or sides of the stomach, nor by heat alone, nor fermentation, nor by the simple resolution of the food into a fluid, but it is evident that it undergoes a series of chemical actions in the stomach and bowels, whereby its nature and properties are completely changed; and thus animal and vegetable substances, however different,

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