IN uu; 



n 



LESSONS IN BOTANY. Ill 



< )N I V.-STBUCTUHE OF T i < >F VEGETABLES. 



-I u vry important point, and helps to furnish n with a 

 mean** t flowering plant*, into two 



. grmijM nr ili\ Ni'iin. !,<! in c.,n- i.lrr that which tukf.-M 

 place doting tlii' growth of an oak t'p>m tin- aoorn. The acorn, 

 on In-ill/ i.lutitt'il in tho ground, sends down its root, and wmcU 

 -t. in. At !ir~t this Btom ia a tiny thing of very incon- 

 rtiili-niblo diameter; year by year, however, it grows, until a 

 gigantic tree n-iiH-<. If wo now cut this tree across and examine 

 ucturo of its section, we shall recognise the following ap- 

 pearances. In tin commencing our examination from 

 without, wo shall find tin- hark, or cortex (Latin, cortex, bark), 

 separable into two distinct layers, the outer of whi' K i 

 thi? culi>-lf (Latin, cutia, skin), or epidermis, (Greek iirttitp/jus, 

 pronounced -, tho outer skin), and tlio inuor ono tho 

 liber, BO called because 

 the ancients occasionally 

 employed this portion of 

 the bark as a substitute 

 for paper in tho making 

 of books liber being tho 

 Latin for book. Passing 

 onwards, wo observe ^ne 

 woody fibre and its cen- 

 trol pith. The woody 

 fibre itself is evidently of 

 two kinds, or at least ia 

 BO put together that wood 

 of two degrees of hard- 

 ness results. Tho exter- 

 nal portion of wood is the 

 softer and lighter in col- 

 our, and termed by bota- 

 nists alburnum, from the 

 Latin word albus, white ; 

 the internal is the harder, 

 and termed by botanists 

 duramen, from the Latin 

 tZiinis, hard, although car- 

 penters denominate it 

 heart-wood. Lastly, in 

 the centre comes the pith 

 or medulla, from the 

 Latin, medulla, the mar- 

 row, which traces its ori- 

 gin to another Latin word, 

 riiedius, tho middle, the 

 marrow being in the mid- 

 dle of the bone. Regard- 

 ing this section a little 

 more attentively, wo shall 

 observe passing from the 

 pith to tho bark, and 

 establishing a connexion 

 between the two, a series 

 of white rays, termed by 

 the botanist mc<i 



greM, the winter to which they are exposed being "o abort, that 

 nine of growth is scarcely interfered with by any im- 

 pediment Under thoe circumntances, there U scarcely any 

 panne Huffioiont to create a line of demarcation between 

 ring and ring ; the progress of deposition goes on oontinuctuly. 

 However, the manner of deposition is not the less external be* 

 cause we cannot see the rings. 



Very different from thi* method of increase U that by which 

 : irrond division of plant* augments in size. For an ex- 

 ample 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 land. If we cut a piece of bamboo, or cane 

 (with which most of OB are familiar), horizontally, we shall find 

 a very different kind of structure to that which we recognised 

 in tho oak. There will be no longer seen any real bark, nor any 

 pith, and tho concentric rays will be also absent, bnt the tissue 

 of which tho stem is made up may be compared to long strings 



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 mat- 

 ter externally, but inter- 

 nally, or, more properly 

 speaking, upwards. A 

 young cane is just as big 

 round as an old cane, 

 tho only difference be- 

 tween them consisting in 

 the matters of hardness 

 and of length. Hence, 

 bamboos, and all vege- 

 tables which grow by 

 this kind of increment, 

 are termed endogenous, 

 from two Greek words 

 ifSov (en'-don), within, 

 and ytvvau (gen-nd-o), I 

 generate. The largest 

 specimen of endogenous 

 growth is furnished by 

 palm trees those magni- 

 ficent denizens of tropical 

 forests to which we are 

 so much indebted for 

 dates, cocoa-nuts, palm- 

 oil, vegetable wax, and 

 numerous other useful 

 product*. Fig. 11 is a re- 

 presentation of the sec- 

 tion of a palm tree, in 

 10. HORIZONTAL SECTION os 1 AN EXooEN. 11. HORIZONTAL SECTION OF AS ENDOGEN. \vhich the peculiarities of 



12. DOTTED VESSELS OF THE CLEMATIS. 13. DOTTED VESSELS OF THE MELON. 11. endogenous Structure OT6 



15. LACTIFEROUS VESSELS OF THE CELANDINE. vory well developed.' 



"" "~ All the endogenous pro- 



ductions of temperate 

 rays, and by the carpenter rilv:r climes are small, though very important. In proof of the latter 



SPIRAL VESSELS OF TEE MELONS. 



16. OVOID CELI. 17. 8TELLIFOHM CELLS. 



grain. We shall also observe that the section displays a series 

 of ring -like forms concentric ono within tho other. These are 

 a very important characteristic. They not only prove that 

 tho 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 tho age of any particular tree the thickness cor- 

 responding with one ring being indicative of one year's growth. 

 Inasmuch as tho formation of an oak tree is thus demo- 

 te be the consequence of a deposition of successive layers of 

 woody fibres externally or without it is said to be 1 

 others subjected to the same kind of growth, an exoyenmts plant 

 from two Greek words, { (eaf-o), without, and ftvvdia (gen- 

 nd-o, g hard, as in gun), I generate. 



Fig. 10 represents tho internal structure of an exogenous 

 stem. 



It is true that tho peculiar disposition of rings thns spoken 

 of cannot always bo recognised. For example, as a rule, trees 

 which grow in hot climates are checked so little in their pro- 



VOL. T 



assertion it may suffice to mention the grosses ; not only those 

 dwarf species which carpet our lawns and our fields with verdure, 

 hut wheat, barloy, oats, rice, maize, all of which aria grasses, 

 botonically considered, notwithstanding their dimensions. In- 

 deed, size has little to do with tho definition of a grass ; for if we 

 proceed to tropical climes, wo shall there find grasses of still more 

 gigantic dimensions. Thns the sugar cane, which grows to the 

 elevation of fifteen or sixteen feet, is a grass, as in like manner 

 ia tho still taller cane, out of tho stem of which, when split, wo 

 make chairbottoms, boskets, 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 page* 

 back, divided vegetables into phomogamons and cryptogamio 

 (we are sure we need not repeat the meaning of those terms). 

 We may now carry our natural classification still further, and 

 say that phamogamous plants admit of division into exogenous 

 and endogenous ones. This division is quite natural, even if w# 



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