NATURAL ARRANGEMENT. 
1053 
Vasculares, Ph/ENogamous, or Cotyledonous plants, are also separated into two great classes called 
Endogencs or Moiiocotyledones, and Exogenes or Dicotyledones, both which are distinguished as accurately 
by their obvious physical structure as they are by the minute and obscure peculiarities of the seed. They are 
ail formed with cellular tissue, woody fibre, and spiral vessels {fig. 2.), and their leaves are traversed by veins ; 
the last character is sufficient for practical purposes, if it is remembered that they also bear perfect flowers, 
(that is, flowers furnished either with stamina, or pistillura, or both,) which will always prevent their being 
confounded with the highest tribes of Cellulares. 
q. Transverse section of a monocotyledonous stem. i, 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. «, Stem and leaves of a monocotyledonous plant. 
Endog;enes, or Monocotyledonous plants, are the first remove from Cellulares, and hold an intermediate rank 
between them and Exogenes 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 Dicotyledones is this, that in Monocotyledones there is only one Cotyledon (fig. 3. s) ; or, if two, that 
they are alternate with each other (t), while in Dicotyledones 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 orig'inate. In Endogenes, or 
Monocotyledones, there is no distinction between wood and bark {fig. 3. q) ; in Exogenes, or Dicotyledones, the 
wood and bark are distinctly separated {fig. 4. v). In Monocotyledones the wood and cellular tissue are mixed 
together without any distinct annual layers of the former being evident ; in Dicotyledones the wood and 
cellular tissue have each their particular limits assigned them, a distinct layer of the former being annually 
deposited. In Monocotyledones there are no radiations from the medulla to the bark ; in Dicotyledones the 
radiations are distinctly marked. In Monocotyledones there is generally no articulation between the leaves 
and the stem, while in Dicotyledones the leaves are always jointed with the stem from which they fall oflT, 
leaving a scar behind. In Monocotyledones the veins of the leaf pass in parallel lines from the base to the apex, 
in Dicotyledones 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. 
TV, An embryo with two cotyledons. z. 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 Phanogamous, 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 take even a morsel of a plant in the hand 
without instantly being in possession of the knowledge of the structure of its seed, with respect to the 
cotyledons. 
Thus far have we advanced v/ithout 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 ovuia, are aids which frequently 
make amends for the absence of fruit : and the nature of the foliage and inflorescence are guides which, 
though sometimes creaclierous, ?re 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 farther in an explanation of 
the manner of determining them ; upon that point each order would require a particular note. It may, how- 
