THE POPULAE EDUCATOE. 



have regard merely to the structure of the stem ; but the 

 agreement is much wider than this, and recognisable by other 

 analogies, as we shall see presently, when we come to consider 

 the nature and peculiarities of leaves and seeds. 



SECTION V. CONCERNING LEAVES AND THEIE USES. 



THERE are two methods of teaching the nature of a thing ; one 

 is by definition, the other by example. Of these the latter is 

 usually the more easy, but the former is the more precise. 

 Accordingly, then, we shall commence by stating that in 

 botanical language a leaf admits of definition as " a thin 

 flattened expansion of epidermis, containing between its two 

 layers vascular and cellular tissue, nerves, and veins, and per- 

 forming the functions of exhalation and respiration." Such is 

 the botanical definition of a leaf. Probably the learner may 

 not understand this definition just yet, but a little contemplation 

 will enable him to do so. With the object of enabling him to 

 understand the definition, suppose we go through its clauses one 

 by one. Firstly, then, a thin flattened expansion of epidermis, 

 we assume to be a self-evident expression. The epidermis 

 means, as we have already stated, the outside bark at least, 

 this is its botanical acceptation. Literally, the Greek word 

 eTriSepfj.ls means skin, as we have said above, and is also applied 

 to indicate that portion of the animal skin which readily peels 

 off, which rises under the action of a blister, and which, when 

 thickened and hardened, constitutes those troublesome pests on 

 the feet which we call corns. As regards the epidermis of 

 vegetables, it may readily 'be seen in the birch tree, from which 

 it peels off in long strips. Well, a leaf, then, consists of two 

 layers of this epidermis, one above and the other below, enclosing 

 vascular and cellular tissue, the meaning of which terms we have 

 now to explain to the reader. The word vascular means " con- 

 sisting of, or containing vessels," and is derived from the Latin 

 vasculum, a little vessel, while cellular, which is derived from 

 the Latin cella, a hollow place or cavity, means, " consisting of 

 cells." By vascular tissue is meant those little pipes or tubes 

 which run through vegetables, just like arteries and veins 

 through animal bodies, and which serve the purpose of con- 

 veying juices from one part of a plant to another. In plants, 

 these pipes or tubes are so exceedingly small that their tubular 

 character is only recognisable by the aid of a microscope or 

 powerful lens, but their presence may be recognised by the 

 naked eye. Thus? for example, we have little doubt that most 

 readers of this work have noticed that, on breaking across a 

 portion of succulent vegetable stem, such, for instance, as a 

 piece of the long stalk of the rhubarb leaf, which is used 

 for making pies and puddings, that the two portions do not 

 always break clean off, but one part remains attached to the 

 other by certain little fibrils. Now, these fibrils are vascular, 

 that is to say, they are tubes, and tubes of various kinds, 

 admitting of distinction amongst themselves. These distinctions 

 we shall not enter upon, here further than stating in general 

 terms that, while some of the tubes are straight, others are 

 twisted or spiral, like the perforator of a corkscrew ; whence 

 arises the term spiral vessels, which botanists have applied to 

 them. Figs. 12, 13, 14, and 15, are magnified representations 

 of the most remarkable kinds of vessels contained in vegetables ; 

 the spiral vessels of which we have been treating will easily be 

 recognised by their peculiar appearance. 



Cellular tissue is, as its name indicates, an assemblage of 

 little cells, the natural form of which is spheroidal or oval 

 (fig. 16), but more frequently this form is modified from variou,s 

 causes, usually the mutual pressure of cells against each other. 

 Thus the pith of trees, a portion of which is made up of cellular 

 tissue, if examined under the microscope, will be found to be 

 composed of cells having the form of honeycomb cells, that is to 

 Bay, hexagonal (fig. 18). 



This last dra-;raig represents the appearance of a thin segment 

 of elder pith when submitted to microscopic examination. 

 Occasionally the cells of cellular tissue assume a star-like or 

 stellate (Latin stella, a star) form, as, for example, is the case in 

 a common bean, of which our diagram (fig. 17) represents a 

 section as seen when examined under the field of a microscope. 

 Usually these vegetable cells are so very small that a micro- 

 scope, or, at least, a powerful lens, is necessary for observing 

 them. In certain vegetables, however, they assume such dimen- 

 eions as to admit of being readily seen by thp naked eye. For 



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, pulled 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 bo suspected to consist of cells. The cuticle of 

 which we have spoken is nothing more than a layer of cells 

 firmly 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 

 cellular tissue. 



We commenced by describing a leaf, but observations have 

 been so often directed to matters collateral to the subject that, 

 the description appears somewhat rambling. Nevertheless, it 

 cannot be helped. 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 

 cuticle 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 

 together, as it does in the substance of a leaf, or as it appears 

 in the orange, then such cellular tissue is denominated paren- 

 chyma, from the Greek word TrapeV^u/xa (pronounced par-en- 

 ku'-ma) " anything poured out." 



Before we quite finish with our remarks relative to the sub- 

 stances which- enter into leaves, it is necessary to observe that 

 the green colouring matter of leaves is termed by botanists and 

 by chemists chlorophyl, from the two Greek words x^vp^s (pro- 

 nounced Jdo-ros), yellowish green, and <f>6\\ov (pronounced 

 Jul'-lon), a leaf. This chlorophyl is subject to become sienna- 

 red in autumn, as we all know, but the cause of this alteration 

 has not yet been explained. 



BEADING AND ELOCUTION. III. 



PUNCTUATION (continued). 

 IV. THE COMMA. 



J 



22. THE mark used for a comma is a round dot ivith a small 

 curve appended to it, turning from right to left. 



23. When you come to a comma in reading, you must, in 

 general, make a short pause or stop, so long as would enable 

 you to count one. 



24. The last word before a comma is most frequently read 

 with the falling inflection 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 yon 

 had read all that you intended to read. 



26. In the following examples keep your breath suspended 

 when you come to the comma ; but let the short pause or stop 

 which you make, be a total cessation of the voice. 



Examples. 



Diligence, industry, and proper improvement of time, are material 

 duties of the young. 



He is religious, generous, just, charitable and humane. 



By wisdom, by art, by the united strength of a civil community, 

 men have been enabled to subdue the whole race of lions, bears, and 

 serpents. 



The genuine glory, the proper distinction of the rational species, 

 arises from the perfection of the mental powers. 



Courage is apt to be fierce, and strength is often exerted in acts of 

 oppression. 



Wisdom is the associate of justice. It assists her to form equ.il 

 laws, to pursue right measures, to correct power, to protect weak- 

 ness, and to unite individuals in a common interest and general 

 welfare. 



Heroes may kill tyrants, but it is wisdom and laws that prevent 

 tyranny and oppression. 



27. When a note of interrogation occurs at the end of a sen- 

 tence, the parts, and even the words, of the sentence separated 

 by commas, should each be read like a question. 



