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ELEMENTARY BOTANY. 



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xxvu 



laterall 



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y as they increase In thickness or breadtli. 



intermixed 



with f)i fiK — --v.^wv. iu W11V.JVUCOO ui uxutnitu. it surruunus or is luxennixeu 



Diants a 11^'^®^^ ^^®y^*^^"^' ^^ ^* may exist alone in some parts of phfienogaraous 



plants, 



•yptog 



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\ll^i! ^J^^^P'^^^^f^^ m^em, or continnous mass of woody and vascular tissue, 

 ceUuiar ! gf^^^a% introduced vertically into, and serves to bind together, the 

 leave/a /? ' ^' xi ^^ ^^^^^^^ued from the stem into the petioles and veins of the 

 i» any SoS*^ pedicels an* parts of the flowers, and is never wholly wanting 



zontfil^fi ^/^«'*™^'^, or outer skin, formed of one or more layers of flattened (hon- 

 or th/pV ™7 ^^^^^^^t» and usually empty cells, with either thin and transparent 

 6utwarL^° opaque walls. It covers almost all parts of plants exposed to the 

 those mrf P^^^^*i°g *lieir tissues from its immediate action, but is wanting in 

 ' 194 n ^^^*^^ P'^^^^^s which are constantly submerged. 

 called' S'/rm ?P^*^^£?^^ i» frequently pierced by minute spaces between the cells, 

 ormore piTk ' ii ®^ ^^® ^^^^ ^^ mouth-shaped, bordered by lips, formed of two 

 close up in !t ^^ disposed as to cause the stomate to open in a moist, and to 



cavitiea an^ ^t^^-^ ^^ *^^ atmosphere. They communicate with intercellular 

 ^ chieflv i ^^% <>bviously designed to regulate evaporation and respiration. They 



1% m ^*^^ J^P^^ leaves, especially on the under surface, 

 ^iiatomical !? ^ P^'^^%'^^<^iis plant has outlived the first season of its growth, the 

 and verv j-^^^^ ^^^^^^^^ stem or other perennial parts becomes more complicated 

 ^°d ^Ht^o<7 ^^^^v.'^^*^^ ^^^ great clusses of phsenogamous plants called Exogens 

 KcotvletW *' which correspond with very Uvr exceptions to the two classes 

 ^Eieng m- f ^^^^*=^C)tyledons (107), founded on the structure of the embryo, 

 central ii /A ^^n ^^^^^' ^^^^ woody system is placed in concentric layers between 

 (Moaocotvled \^i ^^' ^^^ ^^ external separable. Jar* (198, 5). Tn Endogens 

 throug]i the U^i "vvoody system is in separate small bundles or fibres running 

 tinct cpTifr.1^ -fi^ system without apparent order, and there is usually no dis- 



196 Th? ^ f^ '?'*'' "^^^^^ separable bark. 

 ^^ plants. iT+K °^»^^ structure is also somewhat different in the different organs 

 *^e stem vef f K °*' although it is constructed generally on the same plan aa 



Eodogens iq f*.^ ^^g^il^^r organization, and the difference between Exogens and 

 Production of 1 disguised or obliterated by irregularities of growth, or by the 



('^). Ther -Se quantities of cellular tissue filled with starch or other substances 

 ^aacular tissn ^^ ^ T^ if ever, any distinct pith, the concentric circles of libro* 



^%owtK 1 1 ^^^ -^^^g^ns are often very indistinct or have no relation to seasons 



^^7- In th »/ ^P^^e^is has no stomates. 

 the differenced f*^ ^^ branches, during the first year or season of their growth, 

 ^^h there * ?^^^^ Exogens and Endogens is not always very conspicuous. In 

 'ea\ina ^j^ ^^ ^ tendency to a circular arrangement of the iibro-vascular system, 

 l^^ess diatin t t ^^^^- ^^ vacant or filled with cellular tissue (pith) only, and a more 

 poweter th -i?^. ^ ^"^*^ is observable even in several Endogens. More frequently, 

 ^*8 close' Th fiif *^*^*^^ ^® already very apparent the first season, especially towards 

 Passioffn^. X. "bro- vascular bundles in Endogens usually anastomose but little, 

 ^^cular bun ir^7^ ^^*^ *^^ branches and leaves. In Exogens the circle of libro- 

 offsets infn fit^ '*^^^s a more continuous cylinder of network emitting lateral 



*»S^ The w ^''^''^^^^s ^^^ leaves. 



T^^. the ^n^"^^^^^^ ^^^^' ^f*®^ *t« first yea^ ^^i^ growth, consists of 

 ^^^ ^^ the stP ^ cyhnder of celhilar tissue, occupying the centre or longitudinal 

 ^^ comppesT^* ^® active only in young stents or branches, becomes dried up 

 ^^^Qguiahabl * ^^ 1*-.^^ ^^*^^ hardens, and often finally disappears, or is scarcely 



2 the !/ ^ trees. 

 ^^^^ 'fmXnnu'^^ ^^^"^^^^ "^^^^ surrounds and encases the pith. JTt abounds in 

 ^*^l>ranche9 l^u.\ ^ ^^^ ^® ^^ ^ir®<^t connexion when young, with the leaf-buds 

 ^ysteQi, Lik' th ' Petioles and veins of leaves, and other ramifications of the 

 t ^' the Jn^^ ^l*^' ^^ gradually disappears in old wood. 



"^"^^d of ^!i' ^^^^li lies immediately outside the medullary 



^^ously dis^^ - ^^^ (^^^y 2), through which, in most cases, vessels (188, 3) 



sposed are interspersed. ^It is arranged in annual concentric circles 



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