The student may acquire a pretty complete knowledge of the Linnwan artificial sys tem, without knowing much in reality of B.; but, even in beginning to learn the .natural system, he must learn some of the first principles of the ECiellee. Jussieu fol lowed Ray in dividing plants into three great primary divisions—oentyledones (q.v.), monocotyledons (q.v.), and dicotyledones (q.v.); having respectively no cotyledon or seed lobe, one cotyledon, and two cotyledons. And, however the names may be changed, or characters assumed from other parts of the plant, these great divisions of the vegetable kingdom still subsist; the acotyledonous plants being also, according to characters taken from the stem, acrogenous .(q.v.); the monocotyledonous plants, endogenous (q.v.); mid the dicotyledonous plants, exogenous (q.v.). Endlicher is the only botanist of great note who has attempted to make primary divisions of the vegetable kingdom essentially dif ferent from those indicated by Ray, and his attempt has not commended itself to general approval. De Candolle gave expression to an important truth in botanical science, when he united the two divisions of monocotyledonous and dicotyledonous plants under the common title of vascular plants, in opposition to acotyledonous or cellular plants; the vascular plants being the phanerogamous, and the cellular the ergplogamous. Lindley has endeavored to modify the natural system by dividing the asexual or finzreplets (cryp togamous) plants into, 111%1 two classes of the stun and leaves undistin guishable—and with the stem and ]eaves distinguishable, thus limiting the term acrogens to those which have a distinct stem; and in like manner dividing the sexual or flowering (phanerogamous) plants into five classes, viz., rhizogens, with fructi fication springing from a thallus; en.dogens and dictyogens, with fructification springing from a stem, the wood of which is youngest in the center, and the seed with a single cotyledon—the former having parallel-veined permanent leaves, and the wood of the stem always confused; the latter having net-veined deciduous leaves, and the wood of the stem when perennial arranged in a circle around a central pith; gyninogens and tow Ion?, having the wood of the stem youngest at the circumference, and always concentric, the seed with two or more cotyledons; the former having the seeds quite naked, the lat ter having them inclosed in seed-vessels. But others generally prefer the simpler division
of phanerogamous or vascular plants into monocotyledonous of endogenous, and dicot yledonous or exogenous, the former including Lindley's endogens and dietyogens. the latter his exogens, gymnogens, and thizogens; although the latter have only n provisional place assigned them, in the absence of well-ascertained views of their structure.
One of the great advantages of the natural system is, that the plants which it brings together are very generally found to agree in their properties,. as well as in their structu ral characters. There are, indeed, species which, in respect of their properties, aro anomalous or exceptional in the genera or orders to which they belong; but these excep tions do not invalidate the general rule, necording to which we expect the most deadly poisons in the order logankteece, bland mucilage and usefnl fiber in wralnove, wholesome succulent herbage along with a certain amount of acridity or pungency in crueilene, etc., etc. The knowledge of the properties of genera and orders is of great use in guiding and it is thus that modern science attains in rapid succession to discov cries important in their practical relations.
In the determination of the intermediate subdivisions of the natural system, botanists have not yet been so successful as with regard to these primary divisions, and the ascer of the characters and limits of lowest subdivisions—orders, tribes, and genera. Great difficulty has been found iu arranging the orders in natural groups, although the attempt, very necessary to a complete system and a just exhibition of nature, has been very assiduously and perseveringly made by Meisner, Endlicher, Lindley, and others of the greatest botanists of the present age.