494 



NATURAL AIUIANGEMKNT. 



(ttat U, dowrn l\triu»hc\l rithrr «ilh tUnitua, or |ii«tilhiin, or bollO, wliirli will always provont tlu>ir Iumiir 

 •Oaib«llMl(<d Willi Ihr lilK>ir>i ti N ^ , i ( i lltilllrr*. 



Emdifemt$,ot .W»Mt><\>/v «r«- the tir»t remove fVum lVllul^rc>*, ami hoUl an inti'rnnMliatc rank 



bHawu tb*TO ami .•>«i»kj plant*, in wliioli vcKH/ition acquires U« hi({lu'st form of ili-vo. 



lo^MMtlL 'Itirjr werr loi : t< ii»i>l liy having it ^inKlo (-<>t\l(-<l(>ii. hut tliiH circuinKtanco ii* not only 



not ahtululr, but airtliull ..I .!• t. I ii.iuaiion. oxifiit nrti-r minulo anul'ykii. Tlip real (Urtbreiiee in the Hewl <.'( 

 tiMB wmI Lhi-vtyUxluiu u thU, that in Munoiot)Uxlon« tliere it only one rut)kHton (Jig. 3. «) ; or, if two, that 



q, TnuuTrnc wrtion of « monocolvlctlonoun Hem. t, Ri-ctlon of a f^^rminatinK embryo of a emu, lo nhow the two 



r, (irrmliuitian of a monocoljlrdoiumt krvfl. alli niate rot\lo<lonii of tini-<|iial sl/r ; the l>ack and front lolic« 



«, S«i.-tiaa of ditto, to kl>ow the cotjletlon rcmoiuing in the rrprewnt tlnne, the middle lol*c- In the )iUii>uila. 



MM*. u, Stem and leaves of a monocot>ledonous plant. 



they arc alternate with each other (i), while in Dicotylwlons they arc always opposite, and more than one, 

 sometime* several, m in Plima [fig. 4. y). The physiological structure of the' two classes is, however, that t)y 

 which they are familiarly dititinKuished, and exhiliifs a beautiful proof of the harmony that exists between the 

 great features of vegetation and their first princij)le, the seed from which they originate. In EnMgenes, or 

 Mimocofi/li-dons, there is no distinction between wood and bark [^fig. 3.q) ; in Kxdgrn/'^ or DicotylcdonSy the 

 wikkI and bark are distinctly separated JigA. v). In Monocotyledons the wood and cellular tissue are mixed 

 together without any distinct annual layers of the former being evident ; in Dicotyledons the wood and 

 cellular tissue have each their particular limits assigned them, a distinct layer of the former being annually 

 deposited. In Monocotyledons there are no radiations from the medulla to the bark; in Dirotyledons the 

 radiations are distinctly marked. In Monocotyledons there is generally no articulation between the leaves 

 and the stem, while in Dicotyledons the leaves are always jointed with the stem, from which they fall ofT, 

 leaving a scar behind. In Monocotsletlons the veins of the leaf pass in parallel lines from the base to the 

 apex, in Dicotyledons they diverge from the midrib towards the margin at various angles; in the former they 

 are unbranched, the principal veins being connected by nearly simple secondary veins ; in the latter they are 

 much branched, ramifying in many directions, and giving the surface of the leaf a netted appearance. 



V, TransTerse section of a dicotyledonous slein «/, An embryo with many cot^-ledons. 



tv. An embryo with two cotyledons. x, Stem ana leaves of a dicotyledonous plant. 



X, An embryo with four cotyledons. 



Such are the very obvious distinctions of the two great classes of pha?nogamous, or flowering, plants ; and 

 80 far is it from there being any necessity for dissecting a seed in order to ascertain its structure, that this 

 point is one of the most easy determination, and about which there cannot be in one case in five hundred the 

 slightest cause of doubt or difficulty. It is almost impossible to see even a morsel of a plant without instantly 

 being in possession of the knowledge of the structure of its seed, yvith respect to the cotyledons. 



Thus far have we advanced without a single obstacle to impede us. In all farther investigation no greater 

 degree of knowledge or application is requisite than what ought to be possessed by every one who would be 

 able to ascertain the genus of a plant. Many of the orders do not depend upon the minute characters of the 

 seed so much as is believed ; the structure of the ovarium and position of the ovula are aids which frequently 

 make amends for the absence of fruit : and the nature of the foliage and inflorescence is a guide which, 

 though sometimes treacherous, is often as faithful as the fructification itself But as it is not intended to 

 give the characters of the orders in this place, neither is it necessary to advance further in an explanation of 

 the manner of determining them ; uix)n that point each order would require a particular note. It may, how. 

 ever, l>e confidently believed, that there are no greater impediments in the road to an acquaintance with the 

 natural relations of plants than those that have been already removed ; and that although neither the science 



