SERIES III. 
PLANTS EXOGENAE. 
Dicoiyledones , Jussieu. 
Exorhizece, Richard. 
Plants composed of cellular texture, with lymphatic, 
spiral, and proper vessels ; and with cortical pores. Root 
more or less conical, voften without any pith, otherways like 
the trunk. Trunk more or less conical, and composed, at 
least, of two parts growing by different modes, as may be 
best seen in the arborescent species, in which we find 1°. a 
central pith enclosed in a medullary canal, emitting on all 
sides radiating medullary productions ; 2°. annual layers, 
more or less woody, disposed concentrically round the pith, 
the outer layers being the youngest and the least hard ; 
3°. cortical layers, distinct from the wood, but scarcely dis- 
tinguishable from one another, and differing from the last 
in the mode of growth, the inner ones being the youngest, 
and the external being the oldest. Leaves opposite or ver- 
ticillate, sometimes becoming alternate by the growth of 
the stem, disposed more or less spirally on the stem, often 
articulated on the stem, or truly compound ; always fur- 
nished with ribs that anastomose with one another. Flowers 
always distinct, usually furnished with a double perigonium, 
parts usually five in number, or divided into five segments. 
Stamens rarely 3, 6, or 9, or any multiple of 3. Corculum 
most commonly with 2 cotyledons. Coiyledons 2, placed 
opposite, never alternate ; very rarely many, verticillate ; 
and, in leafless plants, none. 
This series contains full two thirds of the whole number 
of natural families ; but the arrangement of these families 
among themselves has not yet been determined, and there- 
fore the families of this series are arranged by De Candolle, 
for the present, into four artificial subseries resting upon 
the differences observable in their petals and stamens, until 
a natural arrangement by their affinities shall be discovered. 
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