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LESSONS IN BOTANY.—III. SECTION IV.-STRUCTURE OF THE STEM OF VEGETABLES. THIS is a very important point, and helps to furnish us with a means of dividing plants, at least flowering plants, into two primary groups or divisions. Let us consider that which takes place during the growth of an oak from the acorn. The acorn, on being planted in the ground, sends down its root, and sends up its stem. At first this stem is a tiny thing of very inconsiderable diameter; year by year, however, it grows, until a gigantic tree results. If we now cut this tree across and examine the structure of its section, we shall recognise the following appearances. In the first place, commencing our examination from without, we shall find the bark, or cortex (Latin, cortex, bark), separable into two distinct layers, the outer of which is termed the cuticle (Latin, cutis, skin), or epidermis, (Greek enidepuis, pronounced ep-i-der-mis, the outer skin), and the inner one the liber, so called because the ancients occasionally employed this portion of the bark as a substitute

for paper in the making of books-liber being the Latin for book. Passing

onwards, we observe the woody fibre and its central pith. The woody fibre itself is evidently of two kinds, or at least is so put together that wood of two degrees of hardness results. The external portion of wood is the softer and lighter in colour, and termed by botanists alburnum, from the Latin word albus, white; the internal is the harder, and termed by botanists duramen, from the Latin durus, hard, although carpenters denominate it heart-wood. Lastly, in

the centre comes the pith or medulla, from the Latin, medulla, the marrow, which traces its origin to another Latin word, medius, the middle, the marrow being in the middle of the bone. Regarding this section a little more attentively, we shall

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gress, the winter to which they are exposed being so short, that their course of growth is scarcely interfered with by any impediment. Under these circumstances, there is scarcely any winter pause sufficient to create a line of demarcation between ring and ring; the progress of deposition goes on continuously. However, the manner of deposition is not the less external because we cannot see the rings.

Very different from this method of increase is that by which another grand division of plants augments in size. For an example we must no longer have recourse to a section of a plant of our temperate zone, but must appeal to the larger tropical productions of this kind. If we cut a piece of bamboo, or cane (with which most of us are familiar), horizontally, we shall find a very different kind of structure to that which we recognised in the oak. There will be no longer seen any real bark, nor any pith, and the concentric rays will be also absent, but the tissue of which the stem is made up may be compared to long strings

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observe passing from the 10. HORIZONTAL SECTION OF AN EXOGEN.

pith to the bark, and

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11. HORIZONTAL SECTION OF AN ENDOGEN.
12. DOTTED VESSELS OF THE CLEMATIS. 13. DOTTED VESSELS OF THE MELON. 14.
SPIRAL VESSELS OF THE MELONS. 15. LACTIFEROUS VESSELS OF THE CELANDINE.
16. OVOID CELI. 17. STELLIFORM CELLS. 18. ANGULAR CELLS.

establishing a connexion
between the two, a series
of white rays, termed by
the botanist medullary rays, and by the carpenter silver
grain. We shall also observe that the section displays a series
of ring-like forms concentric one within the other. These are
a very important characteristic. They not only prove that
the trunk in question was generated by continued depositions
of woody matter around a central line, or, in other words, by an
outside deposition, but they enable us in many cases actually to
read off the age of any particular tree-the thickness cor-
responding with one ring being indicative of one year's growth.
Inasmuch as the formation of an oak tree is thus demonstrated
to be the consequence of a deposition of successive layers of
woody fibres externally or without it is said to be like all
others subjected to the same kind of growth, an exogenous plant
from two Greek words, tw (ex-o), without, and yevváw (gen-
ad-o, g hard, as in gun), I generate.

Fig. 10 represents the internal structure of an exogenous

stem.

It is true that the peculiar disposition of rings thus spoken of cannot always be recognised. For example, as a rule, trees which grow in hot climates are checked so little in their pro

VOL. I.

of woody fibre tightly packed together. These concentric rings, in point of fact, could not have existed; inasmuch as a cane does not grow by deposition of woody matter externally, but internally, or, more properly speaking, upwards. A young cane is just as big round as an old cane, the only difference between them consisting in the matters of hardness and of length. Hence, bamboos, and all vegetables which grow by this kind of increment, are termed endogenous, from two Greek words evdov (en'-don), within, and γεννάω (gen-na-o), Ι generate. The largest specimen of endogenous growth is furnished by palm trees-those magnificent denizens of tropical forests to which we are so much indebted for dates, cocoa-nuts, palmoil, vegetable wax, and numerous other useful products. Fig. 11 is a representation of the section of a palm tree, in which the peculiarities of endogenous structure are very well developed.

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All the endogenous productions of temperate climes are small, though very important. In proof of the latter assertion it may suffice to mention the grasses; not only those dwarf species which carpet our lawns and our fields with verdure, but wheat, barley, oats, rice, maize, all of which are grasses, botanically considered, notwithstanding their dimensions. Indeed, size has little to do with the definition of a grass; for if we proceed to tropical climes, we shall there find grasses of still more gigantic dimensions. Thus the sugar cane, which grows to the elevation of fifteen or sixteen feet, is a grass, as in like manner is the still taller cane, out of the stem of which, when split, we make chairbottoms, baskets, window-blinds, etc., and which, when simply cut into convenient lengths, is also useful for other purposes; one of which will, perhaps, occur to some of our younger readers.

The reader will not fail to remember that we, a few pages back, divided vegetables into phænogamous and cryptogamic (we are sure we need not repeat the meaning of these terms). We may now carry our natural classification still further, and say that phænogamous plants admit of division into exogenous and endogenous ones. This division is quite natural, even if we

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• teaching the nature of a thing; one *** TAND A. Of these the latter is e former is the more precise. Commence by stating that in mita of definition as "a thin termia, containing between its two *--ne, Jerves, and veins, and perluation and respiration." Such is Probably the learner may nat yet but a little contemplation, With the object of enabling him to -pose we go through its clauses one #attened expansion of epidermis, ---vrient expression. The epidermis Aated, the outside bark-at least. Jeptation. Literally, the Greek word care said above, and is also applied the animal skin which readily peels tion of a blister, and which, waen nsututes those roublesome pests on As regards the epidermis of seen in the birch tree, from which Well, a leaf, then, consists of two above and the other below, nclosing the meaning of which terms we have The word ruseniar means "con and is derived from the Latin victim, which is derived from show or cavity, neas, "consisting of is meant those little pipes or tubes Just like arteries and veins wincù serve the purpose of conHaut to another. In plants. twungly smail that their tubular by the aid of a microscope ar cod may be recognised by the habengal's Wer hobre littio loubt that nost * nuced that, on breaking across a m, such, for instance, as a

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an example the reader may refer to an orange, especially an orange somewhat late in the season. If the fruit be cut, or, still better, palled asunder, the cells will be readily apparent. Still more readily do they admit of being observed in that large species of the orange tribe to which the name shaddock, or forbidden fruit. is ordinarily given.

We must now inform the reader that not only do the cells of this cellular tissue admit of being altered in form, but occa sionally they give rise to parts in the vegetable organisation which would not be suspected to consist of cells. The cuticle of which we have spoken is nothing more than a layer of cells irmly adherent: and the medullary rays, or silver grain, of exogenous stems. the appearance of which has been already described, is nothing more nor less than closely compressed ceilniar tissue.

We commenced by describing a leaf, but observations have been so often firected to matters collateral to the subject that the description appears somewhat rambling. Nevertheless, it cannot be heiped. In Botany, above all other sciences, there occur many curious names. They must be learnt, and the best way to teach them is to describe them as they occur.

A leaf. then, we repeat, is an extension of two flat surfaces of enticie enclosing nerves and veins, vascular and cellular tissue. All these terms have been pretty well explained. We may add, however, that when cellular tissue exists confusedly thrown weather, as it does in the substance of a leaf, or as it appears in the orange, then such cellular tissue is denominated parenthyme, from the Greek word rapévxvua (pronounced par-enCanaanything poured out."

Before we quite finish with our remarks relative to the substances which enter into leaves, it is necessary to observe that the green rolouring matter of leaves is termed by botanists and by themists Aurigny), from the two Greek words xλwpós (pronounced is), yellowish green, and púλλov (pronounced qui lon), a leaf. This chlorophyl is subject to become siennain autumn, as we all know, but the cause of this alteration has not yet been explained.

READING AND ELOCUTION.—III. PUNCTUATION (continued).

IV. THE COMMA.

22. Tus na use for a comme is a round dot with a small mrve appended to ut, turning from right to left.

23. When you come to a comma in reading, you must, in general, make a short panse or stop, so long as would enable

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24. The last word before a comma is most frequently read with the falling infection of the voice.

25. In reading when you come to a comma, you must keep your voice suspended as if some one had stopped you before you and read all that you intended to read.

26. In the following examples keep your breath suspended wison you come to the comma; but let the short pause or stop whed you make, be a total cessation of the voice.

Examples.

gene industry, and proper improvement of time, are material Dukes of the young.

smègious, generous, just, charitable and humane.

by wisdom, by art, by the united strength of a civil community, Se enabled to subdue the whole race of lions, bears, and haune glory, the proper distinction of the rational species, Mira the perfection of the mental powers.

es pt to be derce, and strength is often exerted in acts of som is the associate of justice. It assists her to form equal * to pursue right measures, to correct power, to protect weakd to unite individuals in a common interest and general Moon may bil tyrants, but it is wisdom and laws that prevent

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Examples.

Did you read as correctly, speak as properly, or behave as well as James ?

Art thou the Thracian robber, of whose exploits I have heard so mach?

Who shall separate us from the love of Christ? shall tribulation, er distress, or persecution, or famine, or peril, or sword?

How are the dead raised up, and with what body do they come?
For what is our hope, our joy, or crown of rejoicing?

Have you not misemployed your time, wasted your talents, and passed your life in idleness and vice ?

Have you been taught anything of the nature, structure, and laws of the body which you inhabit ?

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The succession and contrasts of the seasons give scope to care and foresight diligence and industry which are essential to the dignity and enjoyment of human beings.

The eye is sweetly rested on every object to which it turns.

Were you ever made to understand the operation of diet, air,It is grateful to perceive how widely yet chastely Nature hath exercise, and modes of dress, upon the human frame?

28. Sometimes the word preceding a comma is to be read like that preceding a period, with the falling inflection of the voice.

Examples.

It is said by unbelievers that religion is dull, unsociable, uncharitable, enthusiastic, a damper of human joy, a morose intruder upon human pleasure.

Nothing is more erroneous, unjust, or untrue, than the statement in the preceding sentence.

mixed her colours and painted her robe.

Winter compensates for the want of attractions abroad by fireside delights and homefelt joys. In all this interchange and variety we find reason to acknowledge the wise and benevolent care of the God of seasons.

32. The pupil may read the following sentences; but before reading them, he should point out after what word the pause should be made. The pause is not printed in the sentences, but it must be made when reading them. And here it may be observed, that the comma is more frequently used to point out the grammatical divisions of a sentence, than to indicate a rest or cessation of the voice. Good reading depends much upon skill and judgment in making those pauses which the meaning of the sentence dictates, but which are not noted in the book; The history of religion is ransacked by its enemies, for instances of and the sooner the pupil is taught to make them, with proper persecution, of austerities, and of enthusiastic irregularities. discrimination, the surer and more rapid will be his progress in the art of reading.

Perhaps you have mistaken sobriety for dulness, equanimity for moroseness, disinclination to bad company for aversion to society, abhorrence of vice for uncharitableness, and piety for enthusiasm. Henry was careless, thoughtless, heedless, and inattentive. This is partial, unjust, uncharitable, and iniquitous.

Religion is often supposed to be something which must be practised apart from everything else, a distinct profession, a peculiar occupation.

29. Sometimes the word preceding a comma is to be read like that preceding an exclamation.

Examples.

How can you destroy those beautiful things which your father procured for you! that beautiful top, those polished marbles, that excellent ball, and that beautifully painted kite, oh how can you destroy them, and expect that he will buy you new ones!

How canst thou renounce the boundless store of charms that

Nature to her votary yields! the warbling woodland, the resounding shore, the pomp of groves, the garniture of fields, all that the genial ray of morning gilds, and all that echoes to the song of even, all that the mountain's sheltering bosom shields, and all the dread magnificence of heaven, how canst thou renounce them and hope to be forgiven!

0 Winter! ruler of the inverted year! thy scattered hair with sleetlike ashes filled, thy breath congealed upon thy lips, thy cheeks fringed with a beard made white with other snows than those of age, thy forehead wrapped in clouds, a leafless branch thy sceptre, and thy throne a sliding car, indebted to no wheels, but urged by storms along its slippery way, I love thee, all unlovely as thou seemest, and dreaded

as thou art!

Lovely art thou, O Peace! and lovely are thy children, and lovely are the prints of thy footsteps in the green valleys.

30. Sometimes the word preceding a comma and other marks, is to be read without any pause or inflection of the voice.

Examples.

You see, my son, this wide and large firmament over our heads, where the sun and moon, and all the stars appear in their turns. Therefore, my child, fear and worship, and love God.

He that can read as well as you can, James, need not be ashamed to read aloud.

I consider it my duty, at this time, to tell you that you have done something of which you ought to be ashamed.

The Spaniards, while thus employed, were surrounded by many of the natives, who gazed, in silent admiration, upon actions which they could not comprehend, and of which they did not foresee the consequences. The dress of the Spaniards, the whiteness of their skins, their beards, their arms, appeared strange and surprising.

Yet, fair as thou art, thou shunnest to glide, beautiful stream! by the village side, but windest away from the haunts of men, to silent valley and shaded glen.

made.

But it is not for man, either solely or principally, that night is We imagine, that, in a world of our own creation, there would always be a blessing in the air, and flowers and fruits on the earth. Share with you! said his father-so the industrious must lose his

hbour to feed the idle.

31. Sometimes the pause of a comma must be made where

Examples.

The golden head that was wont to rise at that part of the table was now wanting. For even though absent from school I shall prepare the lesson. For even though dead I will control the trophies of the capitol. It is now two hundred years since attempts have been made to civilise the North American savage.

Doing well has something more in it than the fulfilling of a duty. You will expect me to say something of the lonely records of the former races that inhabited this country.

There is no virtue without a characteristic beauty to make it particularly loved by the good, and to make the bad ashamed of their neglect of it.

A sacrifice was never yet offered to a principle, that was not made up to us by self-approval, and the consideration of what our degradation would have been had we done otherwise.'

The succession and contrast of the seasons give scope to that care and foresight, vigilance and industry, which are essential to the dignity and enjoyment of human beings, whose happiness is connected with the exertion of their faculties.

A lion of the largest size measures from eight to nine feet from the muzzle to the origin of the tail, which last is of itself about four feet long. The height of the larger specimens is four or five feet.

A benison upon thee, gentle huntsman! Whose towers are these that overlook the wood?

The incidents of the last few days have been such as will probably never again be witnessed by the people of America, and such as were never before witnessed by any nation under heaven.

To the memory of André his country has erected the most magnificent monument, and bestowed on his family the highest honours and most liberal rewards. To the memory of Hale not a stone has been erected, and the traveller asks in vain for the place of his long sleep.

MECHANICS.-III.

FORCES APPLIED TO A SINGLE POINT-PARALLELOGRAM
OF FORCES, ETC.

IN this lesson we have to consider how the resultant of two, and
thence of any number of forces, applied to a single point may be
found. You will keep in mind that by a "single point," I mean
a point "in a body;" and that will save me always adding the
latter words when I use the former. Of course, forces applied
to "a material point" are included in the description, and
theso you will find, in due time, to be of very great importance.

As the joint effect of two or more forces so applied is termed their "resultant," so we name the separate forces of which it is the effect its components. There are thus two operations, the Composition of Forces, and the Resolution of Forces, with which we may be concerned in Mechanics; by the former of which we

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ores, und iraw from and a ne which meet in B, then the Je to C4 En tius formed is the i duvetion, of o r and o q Now, I shall not here give you the strict mathematical proof of this proposition: it is too complicated, and involves so much close reasoning, that to force it on a student in the beginning of a treatise on me Ay diffoulty in his way you have become were and then return to it. In ves that it is true by a ments, one derived from

hts, U V W, be attached to knotted together at o; and

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Long the panapie, then, as estibusted, let us observe its selences. In we pra tan fress, seeing at a point, and you want ther meant Yaka ya vil innefately say, a p-palet gram of the two forces, and me žagoval is the required Le Nut so fast. 7 need not describe the whole of that igure, a part will suffer. Now, if from the end a of o a, you

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a paralei and qui tou a t is tivar you do not want to draw 33 at all. A pve you the far end of the resultant, and all you have to do then is to join E with o, and your object is a gained. This your parallelogram of forces suddenly becomes a triangle of forces; and you may lay this down as your rule in future for compounding two forces.

Fig. 5.

B

Draw from the extremity of one of the forces a line equal, and parallel to, the other force; and the third side of the triargle so formed by joining the end of this line with the point of application is the resultant.

There is great advantage in this substitution of the triangle the third, with their at-, for the parallelogram, for it saves the drawing of unnecessary

lines, which, as you will see, when many forces have to be compounded, would cause much confusion in your figures.

E

R

Fig. 6.

R2

R3

Let us apply this principle now to compound any number of ferees acting on a point. Let there be five, and that will illustrate the rule as well as a thousand could. Suppose forces, o A, O B, O C, O D, O E, applied to the point, o. By the triangular rule, if I draw A R equal and parallel to o B, the line joining o with R is the resultant of the first two forces. I shall not actually draw this line, o R; let us suppose it drawn. Now, if I compound this resultant with o c, I have the resultant of three of the forces. But that, by the same rule, is got by drawing from R a line R R, equal and parallel to o c. The line o R is this resultant of three. Again we shall not draw it. The resultant of this and o D, for the same reason, would be o R, got by drawing R, R, parallel and equal to o D, and, lastly, the resultant of this and o E would be o R3, the line, R, R,, being equal and parallel to o E. We have thus exhausted all the forces, and evidently o R, is the resultant of the whole five. There was here no confusing ourselves with parallelograms; all we had to do was to draw line after line, one attached to the other, carefully observing to keep their magnitudes and directions aright. A kind of unfinished polygon was thus formed, and the line o B,, which closes up the polygon, joining the last point B. with the point of application, is the resultant in magnitude and in direction. Thus you have made another step in advance, and arrived at the Polygon of Forces. You have learned how, by the mere careful drawing of lines, to determine the resultant of any number of forces. All you require is paper and pencil, a rule, compasses, a scale, and a pair of parallel rulers.

Now, there is one point about this polygon I wish you carefully to note. You will observe that the arrows on its sides, representing the directions of the forces you have compounded, all point from left to right, as you go round the figure, turning it with you so as to bring each side in succession to the top. The resultant, however, points in the opposite direction, from right to left, when that side is uppermost. This is as it should be; the direction of the resultant, as you go round the figure, must be opposite to those of the components. The use of this you will see in the next lesson.

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Now, let us suppose that, in determining the resultant after this method, as we come to the end of the operation, the end, B, of the last line, R, R,, chanced to coincide with, or fall upon the point of application, o. The polygon would close of itself without any joining line; what is the meaning of this? means that there is no resultant; the line, o R, is nothing, and therefore the resultant is nothing, and the forees produce equilibrium. What a valuable result we have arrived at! A method by which we can, by rule and compass, tell at once whether any number of forces make equilibrium at a point or not. All we have to do is to describe the polygon of forces, and if it closes up of itself, there is equilibrium; if it does not, there cannot be equilibrium, and the resultant is in magnitude the side which is necessary to close the figure.

Deferring the further expansion of this subject to the next lesson, I shall now turn back and apply these principles to a few elementary examples.

First Example.-Three equal forces act at a point in different directions-what condition should they fulfil in order to be in equilibrium? Get your ruler and compass, and commence constructing the figure by which their resultant may be found. From the end of one of the forces you are to draw a line equal and parallel to the second equal force, and from the end of that another line, equal and parallel to the third. You will thus have three lines strung together, all equal to each other. But if the forces are in equilibrium, the end of the last line must fall on the point of application, that is to say, the polygon of forces must close up, and form a triangle. Your construction will then give you a triangle of three equal sides, commonly called an equilateral triangle. But such a triangle must have

all its angles equal; also the angles between the sides of the triangle, or of the polygon of forces, are the angles between the forces themselves, since they are parallel to these forces. This is evident from the properties, 1 and 2, of the parallelogram referred to above; therefore, in the case we are considering, the three equal forces must act at equal angles, as I showed otherwise must be the case at the close of the last lesson.

R

P

Second Example.-Let a weight hang from the ceiling by means of two cords of unequal length, as in Fig. 7. It is evidently at rest. Whatever be the forces called into action, they produce equilibrium. Is there nothing further to ascertain? There is; it may be desirable to know by how much each cord is strained. Our assurance that the cords will support the weight depends on this knowledge. Let P and Q be the two points of support of the strings which meet at o. Now, whatever be the strains on the cords, O P, o Q, they make equilibrium with w, the weight. Therefore, if we suppose a length, o A, of O P to represent the strain on o P, and from a draw a line, A B, parallel to o Q, equal to the strain, o B, on o Q, then, since the three forces are in equilibrium, the line, R O, closing up the triangle must be equal to, and be in the direction as, the third force, or weight, w. This, then, tells us what to do. Measure on O R upward as many inches as there are pounds in w; and from R then draw RA parallel to

Fig 7.

the cord o q to meet the cord o a. The number of inches in o A will represent in pounds the strain on o P, and those on RA the strain on o q. All, therefore, that we desire to know is determined.

Third Example.-A horse pulls a roller up a smooth inclined plane or slope; what is the force he must exert when he just keeps the roller at rest? And by how much does the roller press on the plane?

B

Let the horse pull in any direction, o A. Then there will be three forces acting on the roller; namely, its own weight right downwards, the horse's pull, and the resistance of the plane or slope, perpendicular to itself. There must be this third force, for the other two, not being opposite to each other, cannot make equilibrium. The roller is somehow supperted by the plane; and that it cannot be unless by its resistance; and plane cannot resist except perpendicu larly to itself. This third force, you thus see, must be

a

Fig. 8.

taken perpendicular to the plane. It is represented in the figure by o B. Now apply the polygon of forces. Let o c represent the weight of the roller, and from c suppose a line, c R, drawn equal and parallel to o A, the horse's pull. Then, since there is equilibrium, the polygon of forces should close up and become a triangle-that is, the line joining R with o should be the pressure, and therefore should be perpendicular to the plane. What then are we to do? Take o c, equal in inches to the number of pounds in the roller, draw then from c a line c R parallel to the horse's pull, to meet the line drawn from the centre o of the roller perpendicularly to the plane; c R so determined will in inches tell the pounds in the horse's pull, and O R the amount by which the roller presses the plane. You can easily see from this that as the slope increases the pull will increase and the pressure diminish. This is what naturally we should expect. The plane I have supposed to be smooth; for, where there is friction against the roller caused by roughness in itself or in the plane, or in both, the question is much altered, as in due time you will see.

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