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ELEMENTARY BOTANY. XXV 



Orders, Genera, and their several 

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>aiuing them according to their evident or presumed importance ; artificial, when 

 . resemwances and differences in some one or very few particulars only are taken into 



T tT ^P'"''^^''*^^ of aU others. ^ ■ ^ 



^no, ihe number of species included in a genus, or the number of genera in an 



mT' \^7^^ variable. Sometimes two or three or even a single species may be so 

 irerent trom all others as to constitute the entire genus : in others, several hun- 

 ea species may resemble each other so much as to be all included in one genus ; 

 moreo ^^^ ^^ r ^^^^ discrepancy in the number of genera to a Family. There is 

 - wheth^^^' ^iprtunately, in a number of instances, great difference of opinion as to 

 of one *^^ cej-tam plants differing from each other in certain particulars are varieties 

 ofsDec^^^^ff^^^*^^^^^^ ^^ distiuct species ; and again, whether two or more groups 

 bibe^ ftf^ '^ n ^^^^^^*^*® ^® many sections of one genus, or distinct genera, or 

 iasuDi^ <^^® Order, or even distinct Natural Orders. In the former case, as a species 

 ment ^^ ^^^ ^ ^^^^ existence in nature, the question is susceptible of argu- 

 8cale of T ^^^^*™^s *^f absolute proof. But the place a group should occupy in the 

 »ore auM^^-^^ ^^ ^^^^ arbitrary, being often a mere question of convenience. The 

 tJ»e stul 7^^?^^ ^^^^ correct principles are multiplied, the more they facilitate 

 Order ai^l f v o ^^' provided always the main resting-poiuts for constant use, the 

 which t" Genus, are comprehensive and distinct. But if every group into 



{ name to P^^ can be divided be erected into a distinct genus, with a substantive 



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I ftOm thp K T-f — ^^*-^^ v*xic:ut;vei- a species is spoiien oi, aii \iU.^ auvci 



|, : ie Dpiitifij simplicity of the Linn^an nomenclature are gone. 





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Chap. III. Vegetable Anatomy akb Physiology. 



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Growth 



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I V 



microscope 



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:.186. Ka'very 



parts are j^^^f parts, forming a sort of honeycombeS structure. " These ultimate 

 the ^nfi>.^ 1 ^ . ^^^» ^^d form by their combination the dtmentarn tissues of which 



187 A ''^i^^* ^« ^^^^^ 

 P^nueableT ^ ^^^ simiJest state is a closed membranous sac, formed of a substaace 

 dividual ^^^^' though usually destitute of visible pores. Each cell is a distinct 

 ^^^ whS» ^f^^^.'^^^^^^y formed and separately acting, though cohering with the cells 

 of whJni, -r I ^^ ^^ contact, and partakinij of the common life and action of the tissue 

 call A - ^t)^ms ii >^ny^^- T*! r.«,t r -.^i.;„^ „- — ^i^„;«,^ +k,. ^r.Mc, o*.,^ ^ic.r» 



(J) ^cfa^^^^^ usually distinguish the foUowiug tissues :— 

 ksa roun 1 • V^^*^^' ^^ i^«''^^^^'^2/»ia, consists usually of thin- walled cells, more or 

 *^riD? af^?/^^^' ^^ ^^^^^ their length not much exceeding their breadth, and not 

 offn,;.? ^ t?e ends. All the soft narts of the leaves, the pith of stems, the pulp 



*^ced an.l ^i. • y^^^S growing parts, are formed of it. It is the first tissue pro 



celb 



plant dies. 



^tive the ^^^ ^^V^® ***^e formed while growth continues, and when it ceases to be 



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XI 



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(2) {j7 y'***;*'<iiea. 



*^^ii broa r ^^*^^*^' ^^ prosenchyma, differs in having its cells considerably longer 

 •^« cells ^^^^^^^y tapering at each end into points and overlapping each other. 

 ^^atitutp^^!i?^^^^^^y thick- walled ; the tissue is iirm, tenacious, and ehujtic, and 

 ^^of le principal part of wood, of the inner bark, and of the nerves and 



(3) Fo*w ^' f^^^iog. in short, the framework of the plant. 

 ^^m thlf ir •^^*'^^' ^^ ^^^ ^<^^^'^ <^^ ^^^^« o^ plants, so called from the mistaken 

 ^^Ummnir « functions are analogous to those of the vessels (veins and arteries) 



iaous planf* ^^- walk obliterated, so as to form a continuous tube. All phc ^^ _ 



*fe tli^ ^ well as ferns and a few other cryptogamous plants, have vessels, and 



^ore called vascular vldnts : so the majority oi cryptogams having only eel- 



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