494 



NATURAL ARRANGEMENT. 



(that is, flowers furnished either with stamina, or pistillum, or both), which will always prevent their being 

 confounded with the highest tribes of Cellulares. 



Endogenes, or Monocotyledonous plants, are the first remove from Cellulares, and hold an intermediate rank 

 between them and Ex6genes or Dicotyledonous plants, in which vegetation acquires its highest form of deve- 

 lopement. They were formerly characterised by having a single cotyledon, but this circumstance is not only 

 not absolute, but difficult of determination, except after minute analysis. The real difference in the seed of 

 them and Dicotyledons is this, that in Monocotyledons there is only one cotyledon {fig. 3. s) ; or, if two, that 



q, Transverse section of a monocotyledonous stem. /, Section of a germinating embryo of a grass, to show the two 



r, Germination of a monocotyledonous seed. alternate cotyledons of unequal size ; the back and front lobes 



s, Section of ditto, to show the cotyledon remaining in the represent these, the middle lobe is the plumula. 



testa. u, Stem and leaves of a monocotyledonous plant. 



they are alternate with each other (t), while in Dicotyledons they are always opposite, and more than one, 

 sometimes several, as in Pinus (fig. 4. y). The physiological structure of the two classes is, however, that by 

 which they are familiarly distinguished, and exhibits a beautiful proof of the harmony that exists between the 

 great features of vegetation and their first principle, the seed from which they originate. In Endogenes, or 

 Monocotyledons, there is no distinction between wood and bark (fig. 3. q) ; in Ex6gene>, or Dicotyledons, the 

 wood and bark are distinctly separated (fig. 4. 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 Dicotyledons 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 off, 

 leaving a scar behind. In Monocotyledons 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, Transverse section of a dicotyledonous stem ,y, An embryo with many cotyledons. 



rv, An embryo with two cotyledons. x, Stem and leaves of a dicotyledonous plant. 



x, An embryo with four cotyledons. 



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

 so 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 strut ture of its seed, with 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 ; upon that point each order would require a particular note. It may, how- 

 ever, be 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 



